By: Author: Browder, Diane M.; Wakeman, Shawnee Y.; Spooner, Fred; Ahlgrim-Delzell, Lynn; Algozzine, Bob
From: Exceptional Children June 22, 2006

This article presents the results of a comprehensive review of 128 studies on teaching reading to individuals with significant cognitive disabilities. The review compared these studies against the National Reading Panel's components of reading; although it revealed an inadequate consideration of the components of reading, it found strong evidence for teaching sight words using systematic prompting and fading. The reviewers considered not only the number of studies, but also indicators proposed for evidence-based practice and effect size. This study identified some high quality studies with strong effect size for comprehension and fluency, but only one phonics study was strong in both quality and effects. Additional research is needed to promote broader skills in literacy for this population.
[Note - The test formatting of this version of the article makes the table difficult to follow. If you are interested in the tables, you'll need to get a hard copy of the magazine or see if you can find the original format of this article online.]

The "science of reading" that has developed over the last 20 years has led to new optimism that, as a nation, we can do better in teaching all students to read (Snow, Burns, & Griffin, 1998). Synthesis reports like Beginning to Read: Thinking and Learning about Print (Adams, 1990), Preventing Reading Difficulties in Young Children (Snow et al.), and Put Reading First: The Research Building Blocks far Teaching Children to Read (National Institute for Literacy, 2001) provide important guidance for teaching reading. Although these reports have relevance for teaching individuals with significant cognitive disabilities, most of the guidelines must be adapted for this population. (The term "significant cognitive disabilities" is used generally in this article to refer to students classified as having moderate or severe mental retardation, who may have additional disabilities such as autism or physical disabilities. The term "mental retardation" is used to refer to the population identified as such in specific research studies or reviews.) Individuals with severe cognitive disabilities may use nonlinguistic communication (Alvares, Falor, & Smiley, 1991) and exhibit learning characteristics that require greater time to learn and intensive forms of instructional support (Westling & Fox, 2000).

Historically, reading instruction for students with significant cognitive disabilities has been underemphasized. Qualitative research including content analyses of textbooks (Katims, 2000) and ethnographic studies of children's school experiences (Kliewer, 1998) reveals a consistent lack of focus on reading. Instead, educators have focused on functional skills reflected in daily living activities. Recently, special educators have emphasized that students with significant cognitive disabilities require intensive instruction in order to learn to read (Browder, Ahlgrim-Delzell, Courtade-Little, & Snell, 2006; Erickson & Koppenhaver, 1995; Kliewer & Landis, 1999). Although these students do need functional skill instruction, reading must be an instructional priority if they are to achieve desired outcomes and make progress. In general, students who do not learn to read have fewer opportunities as adults; not being able to read affects both economic security and general well-being (Chhabra & McCardle, 2004). Educators limit future opportunities if they make an a priori assumption not to teach reading to some students because of the nature or severity of disability.

The Individuals With Disabilities Education Act of 1997 (IDEA) requires that all students with disabilities participate in state assessments and have access to the general education curriculum; alternate assessment must be available for students unable to participate in large-scale testing programs with accommodations. The No Child Left Behind Act (NCLB) requires schools to evidence adequate yearly progress (AYP) in reading (as well as math and science) for all students, including those with disabilities. Subsequent guidelines for NCLB (U.S. Department of Education, December 9, 2003) permit states to use alternate achievement standards for up to 1% of students with significant cognitive disabilities. These alternate achievement standards must (a) be aligned with the State's academic content standards, (b) promote access to the general curriculum, and (c) reflect professional judgment of the highest achievement standards possible. Schools need information on evidence-based practices to set the highest achievement standards possible for reading by students with significant cognitive disabilities.

The National Reading Panel (NRP; 2000), in response to a charge from Congress to assess the status of research-based knowledge in teaching children to read, identified five essential components of reading instruction: (a) phonemic awareness, (b) phonics, (c) fluency, (d) vocabulary, and (e) comprehension. Prior reviews of research on teaching reading to students with mental retardation (MR) reveal a focus on only one of these components--vocabulary; or, more specifically, sight word instruction (Conners, 1992; Houston & Torgesen, 2004). The rationale for teaching sight words is to promote reading for functional use in daily living (Browder, 2001), but few sight word studies have measured either functional use or any form of comprehension (Browder & Xin, 1998). Despite the potential benefit of sight word instruction to promote independence in daily living skills, students also need explicit phonics instruction to become literate (Groff, 1998; Stahl, Duffy-Hester, & Stahl, 1998). Some evidence exists that students with moderate mental retardation can acquire phonics skills (Al Otaiba & Hosp, 2004; Barudin & Hourcade, 1990; Nietupski, Williams, & York, 1979).

Although prior reviews have focused on teaching individuals with mental retardation reading skills (Browder & Xin, 1998; Conners, 1992), additional syntheses are needed for several reasons. First, no reviews on reading distinguished the research specific to individuals with severe mental retardation from that focusing on students with moderate mental retardation. Second, most reviews have not included research on augmentative and assistive communication (AAC) systems to teach symbol reading. AAC research has particular relevance for individuals with significant cognitive disabilities who may be nonverbal and whose first symbol acquisition may be picture symbols. In addition, prior reviews have not organized the literature by NRP reading components. Such an organizational framework can provide clarity about which components of reading require further research. Finally, prior reviews have not provided an evaluation of the quality of research using criteria proposed by research experts (Odom et al,, 2005). The purpose of the current review was to provide a comprehensive synthesis of the research on reading for individuals with significant cognitive disabilities.

METHOD
To make this review relevant for determining evidence-based practices, we organized the literature by reading components, included literature on picture identification (e.g., in AAC use), and evaluated the quality of research using indicators recommended for single subject (Homer et al., 2005) and group research (Gersten et al., 2005) within special education. Our overall research question focused on the extent to which evidence-based practices currently exist for teaching each of the NRP components of reading to individuals with significant cognitive disabilities.

LITERATURE SEARCH PROCEDURES
The research team developed a search list of 362 terms or combinations of terms used by the academic research base to characterize individuals with significant disabilities (e.g., autism, moderate mental retardation, severe disabilities, language arts, reading, literacy, sight words, and phonics). We also included specific program (e.g., Edmark, Distar/Reading Mastery) and instructional procedure terms (e.g., time delay, task demonstration model). The team used these terms to search through electronic and print resources (including InfoTrac, Masterfile Premier, ERIC, PsychInfo, Academic Search Elite, and Dissertation Abstracts; and Education and Training in Mental Retardation and Developmental Disabilities, Remedial & Special Education, and Journal of Applied Behavior Analysis) to identify studies for possible inclusion. The search also included the reference lists of five recent related literature reviews (Browder & Xin, 1998; Conners, 1992; Houston & Torgesen, 2004; Joseph & Seery, 2004; Morse & Schuster, 2004).

INCLUSION CRITERIA
To be included in the review, a study (a) had to be published in a peer-reviewed journal in English between 1975 and 2003; (b) had to include at least one participant with a diagnosis of significant cognitive disability (moderate, severe, or profound mental retardation, autism, or developmental disability); (c) had to have an intervention that targeted teaching reading or picture identification skills as the primary focus and include experimental data; and (d) had to use a recognized experimental or quasi-experimental design (including single subject designs). Although our criteria were overall compatible with the focus on experimental research used by the NRP (2000), it should be noted that single subject research, which comprises most of the research for this population, does not use randomized trials. Thus, we included both experimental and quasi-experimental studies (including single subject research). A total of 128 studies in 119 publications met these criteria (3 articles reported double experiments, and a triple experiment was described in I article).

CODING
Studies that met the criteria for inclusion in the review were then subjected to three rounds of coding: (a) study characteristics, (b) quality indicators, and (c) effect size. We began by coding a large number of study characteristics (n = 96) such as reading content, teaching method, type of prompting, type of reinforcement, setting, instructor, type of data collection design, reliability, procedural fidelity, and number of participants. Two researchers coded a sample of 96 items from 21 randomly selected studies to obtain inter-rater reliability. We used a point-by-point method (the number of agreements for occurrences and non-occurrences divided by the total of points multiplied by 100) to calculate reliability; overall reliability was determined to be 91.3% (range of 85%-97% agreement). Reliability for individual items ranged from 52%-100% with a median reliability coefficient of 95%. (The number of teaching trials was difficult to code with the information given in the articles and was an outlier at 52%; it was not used in further analysis.) We entered coding of all characteristics of the studies into a statistical program (we used SPSS, Inc. software) for ease of summary. Two researchers then classified the components of reading targeted in each study. Inter-rater agreement for these components ranged from 90%-100% across components, with a mean of 93%.

A meta-analysis assessed the effects of the various reading interventions used within the group studies. We used a nonparametric approach to meta-analysis to determine the effects of interventions in the single subject studies. To determine these effects, we calculated the percentage of nonoverlapping data (PND) between the baseline and treatment phases (Scruggs, Mastropieri, & Castro, 1987), and applied the PND to each intervention. We used only the data points in the baseline and intervention phases, because not all studies included generalization or maintenance data. An intervention data point was considered to be nonoverlapping if it was above the highest baseline point. To compute PND, we divided the number of nonoverlapping data points in an intervention by the total number of intervention points for each data series. We analyzed PND averages by reading component, strength of the study as determined by evidence-based practices, and type of disability. We also assessed reliability of PND calculations for 31 of the 88 single subject studies (35%); overall agreement on the PND calculations was 87%.

The effects of the interventions used in the group studies was either the mean difference (d index) effect size (Cohen, 1988) for studies that supplied statistical information about experimental and control groups, or the mean difference (ES index) effect size (Dunlop, Cortina, Vaslow, & Burke, 1996) for studies that supplied statistical information about pretest/posttest groups. Group effect sizes also were analyzed by component of reading and strength of study as determined by evidence-based practice.

To determine the extent to which studies met criteria for being evidence-based, we used the indicators proposed for group (Gersten et al., 2005) and single subject (Homer et al., 2005) designs, because our focus was experimental research. To determine evidence-based practices, we first coded each study against criteria for quality and then determined if there were a sufficient number of studies and participants. We did not need to code information on participants and setting, as the inclusion criteria generated studies that described both these components. To determine the extent to which the single subject studies met the definition of quality described in Homer et al., we clustered the proposed criteria into four rating categories: (a) dependent variable operationally defined and included data on reliability, (b) methods adequately described (independent variable), (c) data on procedural fidelity, and (d) baseline and experimental control (with particular focus on between and within participant replications). Inter-rater reliability for coding quality indicators was established by a point-by-point comparison of these four indicators. All 88 single subject articles (100%) were coded for quality by two of the researchers. The two coders agreed on all codes for all articles except for procedural fidelity that was overlooked by either of the coders for 6 of the 88 articles. This oversight was due to the variety of terms used for the process (e.g., independent variable reliability, procedural reliability). Once the discrepancy was discovered, the coders together determined if the article should receive credit for procedural fidelity.

After coding the individual studies, we considered those that met all criteria and those that omitted only one (typically, omitting measure of procedural fidelity). We identified the specific interventions represented in these studies by reviewing the methods section and looking at SPSS database data summaries of the study's characteristics. Once we identified interventions that occurred across studies, we considered the additional criteria of having been conducted in at least three different geographic locations with three different researchers and including at least 20 participants across studies (Horner et al., 2005).

Similarly for group studies, we applied the Gersten et al. (2005) criteria but clustered these into four categories for coding: (a) outcome measures, operationally defined and evidence of reliability and validity; (b) intervention clearly defined; (c) measure of procedural fidelity; and (d) use of comparison group and their intervention defined. Although Gersten et al. recommend additional criteria (e.g., for data analysis), we found that the subset of criteria applied already eliminated all but a few studies. The authors conducted all coding for quality indicators. Because of the level of judgment required for the coding of the group studies, we used a consensus model to establish reliability: Each study's rating was discussed with one other researcher to ensure agreement as to whether the study should be included in the sets for evidence-based practice. Any studies for which two researchers did not agree were to be submitted to a third researcher, but this did not occur.

RESULTS
Eighty-eight (69%) of the reviewed 128 studies applied a single subject design; 40 (31%) used group design. The first round of coding of study characteristics revealed some general characteristics of this body of research. Most studies (n = 100, 78%) had individuals with moderate mental retardation as participants, 30 studies (23%) had participants with severe mental retardation, and 23 studies (18%) included participants with other types of disabilities.

Total participants (N = 1,123) included 619 (55%) individuals with moderate mental retardation, 124 (11%) individuals with severe mental retardation, 62 (6%) individuals with autism, and 114 (10%) individuals with other cognitive disabilities (e.g., unspecified developmental disability); 204 (18%) participants were not specifically identified as moderate or severe mental retardation. Most of the participants were elementary-age students (5-11; n = 301, 27%); fewer were younger adolescents (12-14; n = 168, 15%) or high school/transition age (15-21; n = 100, 9%). Some participants were adults (n = 50, 4%) and a few were in preschool programs (n = 8, 1%). A number of studies included participants (n = 388) for whom an age range was provided. Finally, a group of studies did not indicate the age of the participants (n of participants = 108). Most of these studies reported a mean age that was in the elementary range (e.g., Calhoon, 2001), but some older studies only provided a mental age (e.g., Dorry & Zeaman, 1975) or no age description (e.g., Guralnick, 1975). Most of the studies (n = 86, 67%) took place in research settings or self-contained special education classrooms. Only a few were implemented in general education classrooms (n of studies = 14, 11%), home (n = 13, 10%), or community (n = 5, 4%). Ten studies (8%) were conducted in other settings (e.g., institution).

The coding of reading components revealed that most of the studies targeted vocabulary, specifically, acquisition of sight words (see Figure 1). Most focused on functional sight words (e.g., Lalli & Browder, 1993; Moseley, Flynt, & Morton, 1997). About a third of the studies targeted picture identification; sometimes this was taught in conjunction with comprehension (e.g., Mackay, Soraci, Carlin, Dennis, & Strawbridge, 2002; Worrall & Singh, 1983). Overall, less than a third contained a measure of comprehension (n = 31, 24%); this was a functional application (e.g., reading a recipe) for 18 of the studies, and an academic application (e.g., reading a story passage) for 13 studies. Only a small number of studies focused on phonics instruction (n = 13, 10%), and fewer still targeted phonemic awareness (n = 5, 4%). Only 36 (28%) studies targeted fluency and most indicators were percentage of errors. No studies were found demonstrating a longitudinal approach to literacy; all studies spanned a few months of a school year and targeted only one or two components of reading. The data in Figure 1 also are divided by type of disability (moderate MR, severe MR, other). Students with severe mental retardation had more vocabulary-focused studies than any other component of reading, but these were split between picture and word studies.

[FIGURE 1 OMITTED]

The second round of analysis considered effect size. For single subject studies, we calculated effect sizes based on PND. Of the 88 single subject studies, 65 articles had sufficient data with a total of 95 PND. Of the 23 studies that did not have sufficient data, 14 studies did not include a graph and 9 studies did not include a baseline. Table 1 includes the number of studies and overall average PND for each reading component. Although studies related to phonics had the highest overall average PND (93%), only three studies addressed that component. Sight word vocabulary was the most frequent component found (41 studies) and had the second highest overall PND average (85%). The most frequent average range of PND for fluency, picture vocabulary, and sight word vocabulary was 81%-90%. The most frequent range for PND for comprehension and phonics was 90%-100%. Overall, these studies had strong effects (highest possible PND is 100% nonoverlapping data points between baseline and intervention).

As Table 2 indicates, there were some slight differences across populations in effect size for these single subject studies. The effect size for vocabulary (picture and word) interventions were lower for students with severe mental retardation (71%-72%), but the same or higher for the other components of reading (for which there were also fewer studies; see Tables 1 and 2).

Only 3 out of 40 group studies provided sufficient information to determine effect sizes (Heimann, Nelson, Tjus, & Gillberg, 1995; O'Connor, Jenkins, Cole, & Mills, 1993; Vandever & Stubbs, 1977). These three studies yielded a total of 20 effect sizes; the average was .994. The range of the effect size measures was -0.16 to 8.33, with a median effect size of .25 and effect size of 1.13 at the 75th percentile. Cohen's (1988) criteria would interpret the median effect size as weak. Six of the 20 effect sizes were negative and from the same study.

After summarizing the studies by component of reading and effect size, the third round of analysis assessed study quality, to determine which interventions met recommendations for evidence-based practice. The criteria recommended for quality within single subject research in special education (Horner et al., 2005) were applied to the single subject design studies. From this analysis, 56 (64%) met all four criteria for quality indicators. An additional 25 (28%) had all criteria except a measure of procedural fidelity, leaving only 7 (8%) studies that missed two or more criteria. Of the 56 studies that met all criteria, 42 (75%) focused on sight word instruction. These 42 studies included 155 participants and were conducted in 9 different geographic locations. As shown in Table 3, of the 42 sight word studies that met all criteria for quality, 38 (90%) used a massed trial training format in which individuals responded to each word presented in succession (e.g., flash card drill). For these interventions, the teacher presented each word or picture, used a defined prompt, and provided feedback on correct responses or errors. Corrected errors received praise and, sometimes, additional reinforcement such as tokens or edibles. When the systematic prompting procedures incorporated time delay, prompts were given before the student could respond, to promote errorless learning (e.g., pointing to the word "bread" while saying "read the word"). Over trials, the prompt faded by increments of a few seconds so that the student would anticipate the correct response (e.g., Collins, Branson, & Hall, 1995; Collins & Griffen, 1996; Lalli & Browder, 1993; Rohena, Jitendra, & Browder, 2002). Nearly all of the studies with a fluency measure focused on error rate. The only evidence-based practice to emerge across studies was the use of time delay to promote errorless learning. Insufficient studies were found to glean evidence-based practices for phonics and phonemic awareness.

In applying Gersten et al.'s (2005) criteria for quality in group design research, only two (5%) studies were found that met all five criteria (Gickling, Hargis, & Alexander, 1981; O'Conner et al., 1993). An additional 19 (48%) were identified that met all criteria except an assessment of procedural fidelity; and two others (5%) met all criteria except having a control group. A wider variation of procedures was used in the group studies, producing no single type of intervention with five or more studies to support it.

Finally, we considered the effect size for single subject studies with Strong indicators for evidence-based practice. Table 4 shows that most studies that reflected all of the quality indicators also had PNDs at or above 80% (strong effects). In contrast, there were exceptions revealing that a study might have all of the indicators of quality, including showing an effect, but not have a strong effect size. If the studies with strong quality indicators' weak effect sizes are discounted, evidence still exists for teaching sight words using massed trial instruction with systematic prompting (see Table 4).

DISCUSSION
While earlier reviews have focused on a meta-analysis of one component of reading (sight words; Browder & Xin, 1998) or broader components of reading without consideration of effect size (Conners, 1992; Houston & Torgesen, 2004), this review did both. Consistent with these prior publications, this review reveals strong evidence for teaching students with significant cognitive disabilities to read sight words using systematic prompting techniques in a repeated (massed) trial format. Uniquely, this review reveals that the studies on teaching sight words to students with severe mental retardation are also of sufficient number, quality, and effect size to conclude that this intervention is effective for this population as well as for students with moderate mental retardation. Our review of studies on teaching picture or symbol identification also revealed that students with severe mental retardation can learn symbols related to literacy. What is lacking in the evidence to date is how to teach students with either moderate or severe disabilities the other components of reading needed for literacy.

Researchers have found that phonemic awareness and letter knowledge are the best school-entry predictors for how well children will learn to read in the first 2 years of instruction (Ehri, 2004; Share, Jorm, MacLean, & Matthews, 1984). Juel, Griffith, and Gough's (1986) meta-analyses found solid support that phonemic awareness instruction was more effective than alternative forms of instruction (or no instruction) in teaching students to read. Similarly, in a meta-analysis, systematic phonics instruction helped children learn to read more than nonsystematic phonics or no phonics instruction (Juel et al.). In a comprehensive review of reading research for students with mental retardation, Conners (1992) found only seven studies (19% of those reviewed) that included phonics instruction. In a recent update, Joseph and Seery (2004) identified seven additional studies. Most participants in the extant research had mild mental retardation and most of the work focused on demonstrating a small subset of phonics skills rather than mastering decoding. In the current review, only a few studies were found that focused on phonics and phonemic awareness (see Figure 1) and an insufficient number of these met criteria for evidence-based practice in special education (Gersten et al., 2005; Homer et al., 2005). Interestingly, the few phonics studies found that could be coded for effect size were strong (see Table 1). Only three studies were found that focused on phonics for students with severe mental retardation (Basil & Reyes, 2003; Hoogeveen & Smeets, 1988; Hoogeveen, Smeets, & van der Houven, 1987), but the one of these for which an effect size could be computed (Hoogeveen et al., 1987) had a strong effect size (PND = 100%)

Clearly, the need exists for research on how to teach phonemic awareness and phonics to individuals with significant cognitive disabilities. The lack of focus on this type of instruction may reflect prior expectations that this population might acquire a sight word vocabulary, but would not learn to read. Given that research has shown a lack of exposure to reading for this population (Katims, 2000; Kliewer, 1998), the potential impact of an explicit phonics program is unknown. A few clues can be derived from the small body of phonics studies using (a) an individualized, repeated trial format in which students receive multiple opportunities to make the target response (Barbetta, Heward, & Bradley, 1993; Barudin & Hourcade, 1990; Lane & Critchfield, 1998); and (b) low-tech (sandpaper letters, visual graphics) and high-tech (computer-assisted instruction) accommodations to promote responding (Barudin & Hourcade; Lane & Critchfield). These interventions should be viewed with caution, given the lack of sufficient studies and small number of participants.

One complication that arises in teaching phonemic awareness and phonics to this population is that many of the students rely on alternative and augmentative communication (AAC). Instruction in phonemic awareness and phonics often relies on students producing sounds in letters and words. While our review did not identify research on students who are both nonverbal and have significant cognitive disabilities, research with students with physical disabilities reveals that decoding can be taught using a nonverbal approach (Coleman-Martin, Heller, Cihak, & Irvine, 2005; Heller, Fredrick, Tumlin, & Brineman, 2002). The need exists for research extending these nonverbal approaches to this population.

Although comprehension is the ultimate goal of reading instruction, teachers spend little time teaching it (Hodges, 1980). In analyzing 203 studies of comprehension strategies, the NRP (National Institute of Child Health and Human Development, 2000) reported efficacy for eight practices: (a) comprehension monitoring, (b) cooperative learning, (c) graphic organizers, (d) story structure, (e) questioning, (f) question answering, (g) question generation, and (h) summarizing. Although research on reading comprehension has a long history, it is not as far along as research on other aspects of literacy (Perfetti, 1985; cf. Snow et al., 1998). Current knowledge about reading comprehension supports including comprehension-specific instruction in any literacy program. For example, students who perform better on comprehension tasks also demonstrate better decoding skills, global language skills, and oral reading fluency; and, elements of reading comprehension--the text, the activity, and the reader--interact in ways that influence how learners interpret and transmit information (Franklin, Roach, & Clary, 1992; NRP,, 2000).

In our review, we found 23 reading studies that measured or taught comprehension to individuals with moderate and severe MR. Eleven of these studies included participants with severe MR (e.g., Anderson, Sherman, Sheldon, & McAdam, 1997; Fiscus, Schuster, Morse, & Collins, 2002; Mechling & Langone, 2000; Romski, Sevcik, Robinson, Mervis, & Bertrand, 1996). While only about half (n = 11) of these 23 studies met the criteria for quality, this collection had an overall strong effect size and enough studies to glean some information on evidence-based practice. Most of the high quality studies addressed comprehension through having the student use a sight word in the context of a functional activity (e.g., Browder & Minarovic, 2000; Fiscus et al.; Kyhl, Alper, & Sinclair, 1999; Mechling & Gast, 2003). In others, individuals demonstrated comprehension through word-to-picture matching (e.g., Driscoll & Kemp, 1996; Eikeseth & Jahr, 2001; Mechling, Gast, & Langone, 2002; Rehfeldt, Latimore, & Stromer, 2003). In some of the research, individuals received systematic instruction to make the comprehension responses through massed trial training (e.g., to match picture and word) with systematic prompting and fading (Browder, Hines, McCarthy, & Fees, 1984; Browder & Minarovic; Collins et al., 1995; Doyle & Gast, 1990). While these studies provide overall evidence for addressing comprehension through concrete means (using a picture or activity) with stimulus control procedures, they fit into only one of the eight effective strategies for comprehension. That is, they rely on question answering. The need exists for research that will expand interventions in comprehension to address the other practices identified by NRP.

Reading that is considered fluent is accurate, completed at a reasonable rate, and prosodic (Kuhn & Stahl, 2003). Guided oral reading is one way to help students become more fluent readers (Stahl, 2004; Therrien, 2004). Studies with students with mild disabilities have focused on building fluency through timed repeated readings and other simple practice methods; assessment largely has used timed reading probes. In our research, we found most studies with a fluency focus Simply measured error rate to document that the stimulus control procedure designed to produce errorless learning achieved this goal (Browder & Minarovic, 2000; Farmer, Gast, Wolery, & Winterling, 1991; Hoogeveen, Birkhoff, Smeets, Lancioni, & Boelens, 1989; McGee & McCoy, 1981; Stinson, Gast, Wolery, & Collins, 1991). A small number of studies contained measures of counting words read correctly from passages, by individuals with moderate MR (Singh & Singh, 1984, 1985, 1988; Singh, Winston, & Singh, 1985). For the most part, research on individuals with significant cognitive disabilities has occasionally measured fluency, but rarely taught this component of reading.

Research has shown that reading ability and vocabulary size are related, but the causal link has been difficult to demonstrate (Stanovich, 2000). Because of the sheer volume of vocabulary in children's literature, educators have sometimes relied on context for these concepts to emerge (Kamil, 2004). The NRP review (2000) showed that although context is important, direct instruction in vocabulary improves both vocabulary and comprehension. The strongest research to date on teaching individuals with MR to read uses stimulus control procedures for sight word vocabulary (Houston & Torgesen, 2004). In a meta-analysis of sight word instruction, Browder and Xin (1998) found that most of the 48 studies conducted since 1980 were with students with moderate mental retardation and that, overall, sight word instruction had been highly effective. Their meta-analysis, along with Browder and Lalli's (1991) review, showed a prevalence of stimulus control procedures for sight word instruction (Barudin & Hourcade, 1990; Browder et al., 1984; Browder et al., 1990; Karsh, Repp, & Lentz, 1990; McGee, Krantz, & McClannahan, 1986). The current review is consistent with earlier work in that the predominance of sight word studies relied on systematic prompting procedure. What this review uniquely reveals is there are also enough studies with students with severe mental retardation to conclude that this population can learn sight words with systematic prompting like time delay.

CONCLUSIONS AND NEEDS FOR FUTURE RESEARCH
Consistent with prior reviews of reading instruction for this population (Browder & Xin, 1998; Conners, 1992), we found the strongest evidence for teaching sight words using systematic prompting such as time delay. Some evidence also exists for teaching comprehension using concrete referents like pictures, or an activity to demonstrate understanding of the word. The least is known about phonics and phonemic awareness. Some researchers have measured fluency as error rate, but rarely have researchers taught fluency. This review uniquely highlights that the overall same conclusions can be made for students with severe mental retardation as for those with moderate mental retardation; students with severe mental retardation also can learn to identify and comprehend sight words using systematic prompting methods with concrete referents.

This review is also one of the first to apply the quality indicators proposed by Horner et al., (2005) for single subject research and Gersten et al. (2005) for group research in special education. We found there were two important considerations in applying these quality indicators. First, we discovered the importance of evaluating the research design's quality indicators in conjunction with effect size. Not all studies with high quality have strong effects, and vice versa. Second, we divided the indicators into discrete categories, as described earlier, to use them in coding the studies. In applying the criteria, it also was evident that the quality of research in special education has generally improved over time. For example, implementing and describing procedural fidelity was frequently lacking in the earlier research. A limitation of our use of quality indicators is that nearly all of our conclusions were drawn from single subject research. Group research with this population has been sparse, not consistent with current indicators of quality, and offers insufficient data to compute effect size, or reveals weak effect size.

Although the strong areas of research on reading instruction for this population show us how to do what we have done well (sight words), they do not yield sufficient guidance for the future. As noted earlier, the "science of reading" developing in the last 20 years has led to optimism about teaching all students to read (Snow et al., 1998). In the past, criteria such as severity of disability (e.g., IQ) or student need for functional skills were used to determine whether to teach reading to students with significant cognitive disabilities. When reading was included in instruction of these students, the focus was typically sight words, used in the context of functional activities.

Some case studies provide evidence that students with significant cognitive disabilities can acquire broader literacy skills. For example, Koppenhaver, Erickson, and Skotko (2001) found that storybook reading promoted communication for children with Rett syndrome. Through a series of qualitative studies, Kliewer and Biklen (2001) found that students with severe disabilities' skills with printed language proceeded from their social engagement, often taking the form of localized conversation. For example, to support a student in telling a story, the teacher had the student's parents send in snapshots and notes of her activities at home. Her classmates without disabilities used these to help her compose a story. They noted that she progressed from short utterances to being able to express ideas as their work progressed. The student's developing keyboard skills on a specially designed computer system reflected her emerging literacy skills. Ryndak, Morrison, and Sommerstein (1999) described a case study in which a girl with a significant cognitive disability learned to read and write through participation in general education. These case studies provide important examples of comprehensive reading instruction that led to increased literacy. One direction for future research would be to use the guidelines from these case studies to develop future experiments on teaching individuals with significant cognitive disabilities. These studies suggest that reading interventions for this population may need a social communication component. Sharing stories is one way to promote reading skills such as comprehension, vocabulary, and fluency in a meaningful context.

A second way to build a reading intervention for future evaluation is to apply the evidence from current research to other components of reading. The strongest evidence for this population shows that systematic prompting and fading with many opportunities for the student to practice the response has been effective for teaching sight words and some comprehension skills. Future research may replicate this systematic instruction in teaching phonemic awareness and phonics skills. It may be important to provide direct instruction for students to generalize these skills to story reading and other activities to give them meaning.

Research is also needed on longitudinal reading instruction. For most children, reading skills build across years. Reading research for individuals with significant cognitive disabilities has focused on the acquisition of a specific set of skills (e.g., recipe sight words) in a short time period. More research is needed to determine how to promote reading skills across years of instruction. Ryndak et al.'s (1999) case study suggests potential benefits for implementing this instruction in a general curriculum context.

IMPLICATIONS FOR PRACTICE
This review provides evidence that using systematic prompting and fading procedures like time delay to teach sight word reading and comprehension to individuals with significant cognitive disabilities has the strongest research evidence for effectiveness. Sight words can provide an important resource for daily living, such as being able to follow a job sequence (Browder & Minarovic, 2000) and perform activities such as cooking (Browder et at., 1984) or grocery shopping (Kyhl et at., 1999). In learning to read English, irregular words do not lend themselves to decoding and must be acquired as sight words. Providing repeated trial instruction on sight words can build vocabulary as part of a reading program.

The more difficult question for practice is how to address phonemic awareness and phonics. Research on phonemic awareness supports its critical role in learning to read (Juel et al., 1986). The lack of research on phonemic awareness and phonics, along with research showing this population has often had minimal reading instruction (Katims, 2000; Kliewer, 1998), suggests that students with significant cognitive disabilities may not have learned to read in the past because they were either not taught to read or were not taught with methods that promote literacy. The questions for future practice are how to teach these skills and how long to continue this instruction. Published curricula for phonemic awareness may not be chronologically age-appropriate for older individuals. No direction exists for how long this population may need to learn these skills. This lack of evidence on how to teach the skills that lead to decoding in reading points to the importance of making individual decisions about student progress. Although it is important for practitioners to collect ongoing data for educational decision making in general, it is especially critical to have these data to make decisions about reading instruction with the student and his or her family.

Because of the lack of focus on reading instruction for this population in the past (Katims, 2000; Kliewer, 1998), the potential outcomes are unknown. Case studies provide examples of this population gaining literacy skills (Koppenhaver et al., 2001; Ryndak et al., 1999). This review has offered evidence from experimental research that individuals with significant cognitive disabilities can learn to read sight words with systematic instruction like time delay. The next step is to involve individuals with significant cognitive disabilities in comprehensive, longitudinal literacy instruction that focuses on all components of reading, including the decoding skills that promote learning to read. Future research and practice might indicate that interventions used with students without disabilities are effective for individuals with significant cognitive disabilities (e.g., explicit phonics instruction), or that this population needs unique forms of support to learn to read (e.g., inclusive social context or repeated trial instruction)--or both.

Correspondence concerning this article should be addressed to Diane Browder, Department of Special Education and Child Development, University of North Carolina at Charlotte, 9201 University City Blvd., Charlotte, NC 28223. (e-mail: dbrowder@email.uncc.edu)

Support for this research was provided in part by Grant No. H324D020027 from the U.S. Department of Education, Office of Special Education Programs, awarded to the University of North Carolina at Charlotte. The opinions expressed do not necessarily reflect the position or policy of the Department of Education, and no official endorsement should be inferred.

Our thanks to Steve Graham, Editor, for recommending that we compare effect size and quality indicators.

Manuscript received May 2005; accepted October 2005.

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DIANE M. BROWDER

SHAWNEE Y. WAKEMAN

FRED SPOONER

LYNN AHLGRIM-DELZELL

BOB ALGOZZINE

University of North Carolina at Charlotte

DIANE; M. BROWDER (CEC NC Federation), Snyder Distinguished Professor of Special Education, Department of Special Education and Child Development; SHAWNEE Y. WAKEMAN (CEC NC Federation), Research Associate, Department of Educational Leadership; FRED SPOONER (CEC NC Federation), Professor, Department of Special Education and Child Development; LYNN AHLGRIM-DELZELL, Research Associate, Department of Special Education and Child Development; and BOB ALGOZZINE; (CEC NC Federation), Professor, Department of Educational Leadership, University of North Carolina at Charlotte.

TABLE 1
Number of Studies, Overall Mean, and Frequency for Percentage of Nonoverlapping Data Points (PND) by Component of Reading
Number of Studies With PND of 60%
Component of Reading Frequency Mean PNDor Below
Vocabulary: Pictures 1681% 2 (12.5%)
Vocabulary: Sight words4185% 2 (4.9%)
Phonics 393% 0 (0.0%)
Phonemic awareness 0 0 0
Comprehension 2084% 2 (10.0%)
Fluency2081% 2 (10.0%)


NumberNumber of Studiesof Studies With PND With PND Component of Reading of 61%-70%of 71%-80%
Vocabulary: Pictures1 (6.3%) 3 (18.8%)
Vocabulary: Sight words 1 (2.4%) 7 (17.1%)
Phonics 0 (0.0%) 0 (0.0%)
Phonemic awareness 0 0
Comprehension 1 (5.0%) 3 (15.0%)
Fluency 0 (0.0%) 3 (15.0%)


NumberNumber of Studiesof Studies With PND With PND Component of Reading of 81%-90%of 91%-100%
Vocabulary: Pictures6 (37.5%) 4 (25.0%)
Vocabulary: Sight words19 (46.3%)12 (29.3%)
Phonics 1 (33.3%) 2 (66.7%)
Phonemic awareness 0 0
Comprehension 5 (25.0%) 9 (45.0%)
Fluency12 (60.0%) 3 (15.0%)
Note. More than one component of reading may occur within a study.

TABLE 2Br> Reading Components and Mean Percentage Nonoverlapping Data Points (PND) by Type of Disability
Vocab-SW
# of# of
Type of SS # of PNB M
Disability Studies Studies Studies PND
Moderate MR 67 52 38 85
Severe MR 15 6 3 72
Other 19 7 5 81


Fluency
# of
Type of # of PND M
Disability Studies Studies PND

Moderate MR 26 20 81
Severe MR 4 2 84
Other 3 1 77

Vocab-Picture


# of
Type of # of PND M
Disability Studies Studies PND

Moderate MR 14 9 80
Severe MR 8 4 71
Other 7 5 84

Comprehension
# of
Type of # of PND M
Disability Studies Studies PND

Moderate MR 14 10 82
Severe MR 7 4 93
Other 9 9 75

Phonics

# of
Type of # of PND M
Disability Studies Studies PND

Moderate MR5 3 93
Severe MR 2 1 100
Other 0 00

Note. SW = sight word. Studies may have included more than one type of disability and component of reading. Phonemic awareness is not included in the table. "Other" category includes autism and developmental delay. SS = single subject.

TABLE 3
Reading Components Reflected in Evidence-Based Single Subject Studies
Number of Studies Studies Meeting Supporting Component All Quality Evidence-Based Evidence-Based of Reading Indicators Practice Practice
Vocabulary:
Sight words 42Massed trial 38 (90%)
Time delay 24 (57%)
Systematic 26 (65%)
prompting
(besides delay)

Vocabulary:
Pictures 14Massed trial 9 (64%)
Systematic 8 (67%)
prompting
(varied)

Comprehension 14Massed trial 9 (64%)
Systematic 7 (50%)
prompting
(varied)
Pictures 4 (33%)
Functional use14 (100%)

Fluency 25Time delay12 (48%)
(error rate (for low error studies rate)

Phonics 1 (a) (a)

Phonemic Awareness 0 (a) (a)


Number Participants of Demonstrating ComponentEvidence-Based Geographic Evidence-Based of Reading Practice Locations

Vocabulary:
Sight words Massed trial9 155
Time delay 4 96
Systematic 6 92
prompting
(besides delay)

Vocabulary:
Pictures Massed trial5 36
Systematic 6 27
prompting
(varied)

Comprehension Massed trial5 37
Systematic 5 31
prompting
(varied)
Pictures2 14
Functional use 7 55

Fluency Time delay 4 44
(for low error rate)
Phonics (a)(a)(a)
Phonemic Awareness (a)(a)(a)

(a) Too few studies meeting quality indicators to reliably attribute or support evidence-based practice.

TABLE 4
Effect Size for Single Subject Studies With Strong Indicators for Evidence-Based Practice, by Reading Component
Effect Size for Studies Meeting Quality Indicators (n = 44)

Number of Studies Percentage Number/
Meeting With PND Percentage
Components Quality of 60%With PND of
of ReadingIndicators or Below 61%-70%
Phonics (n = 1)0 (0.0%)0 (0.0%)
Comprehension (n = 11)0 (0.0%)1 (9.1%)
Vocabulary:
Sight words (n = 32)2 (6.3%)1 (3.1%)
Vocabulary:
Pictures (n = 11)2 (18.2%) 1 (9.1%)
Fluency(n = 18)2 (11.1%) 0 (0.0%)


Effect Size for Studies Meeting Quality Indicators (n = 44)

Strong Effects
Number/ Number/ Number/
Percentage Percentage Percentage ComponentsWith PND of With PND of With PND of of Reading 71%-80% 81%-90%91%-100%
Phonics 0 (0.0%) 0 (0.0%) 1 (100.0%)
Comprehension 1 (9.1%) 3 (27.3%) 6 (54.5%)
Vocabulary:
Sight words 4 (12.5%) 16 (50.0%) 9 (28.1%)
Vocabulary:
Pictures1 (9.1%) 6 (54.5%) 1 (9.1%)
Fluency 2 (11.1%) 11 (61.1%) 3 (16.7%)

Note. More than one component of reading may occur within a single study. Phonemic awareness is not included in the table due to insufficient data. Only studies that included all of the quality indicators for single subject research are included in this table.

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