Current Status of Treatments for Dyslexia: Critical Review

Ann W. Alexander, MD; Anne-Marie Slinger-Constant, MD

Disclosures

J Child Neurol. 2004;19(10):744-758. 

In This Article

Current Research

This article focuses on research studies that compare treatment efficacy for prevention (ie, working with young children who are "at risk") and the efficacy of various approaches to remediation (ie, treating older children who have already been identified as reading disabled). Pre- and post-treatment functional brain imaging studies have been conducted in some of these studies, and these are discussed. Behavioral studies in combination with neuroimaging studies allow us to develop an understanding of the neurobiologic correlates of behavioral responses to treatment. Finally, development of computational models, computer simulations of how reading is acquired, has not only provided additional insight into the process of reading acquisition but has also offered explanations for specific intervention outcomes.[4]

Torgesen, in an overview of research on the effectiveness of interventions with at-risk children, in the classroom and with small groups, noted that two programs providing relatively direct, systematic instruction in phonemic decoding skills, "Direct Instruction" and "Success for All," were effective for this at-risk group but not for already impaired readers.[1] Tunmer and Chapman conducted a longitudinal study using the Reading Recovery Method, which has been a popular early intervention program in the schools.[5,6] It offers one-to-one, daily, pull-out tutoring for 12 to 20 weeks for 6-year-old children performing at or below the 30th percentile in reading. Although it has been reported to be helpful for struggling readers, its effectiveness has not been documented by rigorous research. Tunmer and Chapman found that 30% of the children were referred out of the program because they were not responding.[5] These children were found to have significant phonologic deficits, which probably accounts in part for their lack of response. When the children who did show a good response to the intervention at the end of the treatment were tested 1 year later, their performance was no better than that of the controls. These findings indicate that intensive treatment alone is not enough; despite one-to-one instruction, the at-risk children did not respond as well as those receiving appropriate classroom intervention. This study illustrates that the content or method of intervention is itself a critical factor in treatment efficacy. The Reading Recovery Method is a top-down, more whole-language approach using semantic or syntactic clues for word reading and does not contain the explicit phonics or phonologic awareness instruction needed by these younger at-risk children.

Denton and Mathes reported the effectiveness of four primary classroom treatment projects that followed the National Reading Panel recommendations.[7] The study targeted at-risk children who fell between the 18th and 25th percentiles in phonologic and letter knowledge skills. After intervention, 18 to 31% of the children still had not reached the benchmark of the 30th percentile for word-level reading and would require a higher level of intervention. Denton and Mathes also evaluated the effectiveness of five interventions that involved a more intensive approach (one to one, small group with more hours of instruction) with students who were more impaired (12–18th percentile). They found that 4 to 30% remained below the 30th percentile benchmark after this treatment. On extrapolating their findings to the general population for both groups, they noted that only 0.7 to 4.5% of the more severely impaired group and 5 to 6% of the mild to moderately impaired group remained in the impaired range, a significant difference from the 15 to 20% rate currently reported. Both types of intervention yielded significant results, with the more intensive administration moving even the more severely at-risk children into the average range.

Torgesen and colleagues conducted a study of kindergartners who were severely at risk (10th percentile for prereading skills).[8] The study compared the effect of three types of intensive interventions that were delivered.one on one, 20 minutes/day, and 4 days/week through the end of second grade. There was also a no-treatment control group. The interventions were (1) a regular classroom reading curriculum, which was more whole language in nature; (2) embedded phonics training, which provided more implicit, nonsequential phonics instruction when the opportunity presented itself in text; text reading and writing instruction were the predominant component; and (3) an explicit, sequential direct teaching of phonemic awareness using a multisensory approach, which brought in the motor perception of speech sounds (the Lindamood Auditory Discrimination in Depth program)[9] to facilitate the development of fine-grained phonemic representations. Decoding and encoding of words with direct phonics instruction comprised most of the instruction, with little emphasis on text reading. This approach was a predominantly bottom-up, sensory approach for the development of more distinct phoneme representations, in contrast to the more top-down orthographic-semantic approach of the other interventions. It also offered more explicit phonics instruction.

The bottom-up, sensory, more explicit approach was significantly superior to all of the other groups at the end of the intervention period. The more top-down interventions resulted in outcomes similar to those of the no-treatment controls. Long-term follow-up revealed that the more explicitly trained group (those receiving the Lindamood Auditory Discrimination in Depth program) was performing solidly in the average range for accuracy and fluency at the end of the fourth grade. These findings suggest that these young, impaired children required much more salient intervention to improve their phoneme maps, combined with explicit instruction for letter and sound mapping. The more implicit phonics approach that taught phonics rules was ineffective. Perhaps this was due to the more abstract, top-down nature of teaching the phonics rules, without establishing fine-grained phonemic representations. With deficient phonologic processing, less explicit instruction would place greater demands on executive function. Because neither executive function nor abstract thinking ability is fully developed at this younger age, a more concrete intervention program would be expected to be most effective for the struggling reader.

Denton and Mathes also addressed the question of which criteria are most useful for predicting success with future reading acquisition following early intervention.[7] They found that fluency (or words read per minute) was more significantly related to future outcome than other reading measures, and the rate of response to intervention was also a predictor of future reading development—the slower the learning curve, the more difficult it was for the child to become an adequate reader.

Vellutino and colleagues also found the rate of response to treatment to be a significant predictor of outcome. Their 6-year longitudinal study of at-risk first-graders revealed that the children in the "limited response to intervention" group (treatment resisters) differed from the children who were readily remediable.[10] Although all of the subjects had significant difficulty with phonologic skills such as phoneme awareness and with letter and number naming, there were differences between the readily remediated readers and the most difficult-to-remediate readers in their cognitive and language-based abilities.rapid naming, confrontational naming, verbal working memory (syntactic word order, nonword repetition), short-term verbal memory (digit span), and articulation speed. The readily remediated group performed more like the normal reading group on these measures. These children were more likely to have had limitations in their early language experiences and/or instruction. Thus, although all of the children had phonologically based deficits, there were two different types of deficient phonologic sensitivity. One group lacked the environmental exposure necessary for the development of a strong phonologic system (an "experiential reading disability"); the other group of children had been exposed to appropriate environmental stimulation but had atypical development of the neural systems underlying phonologic sensitivity (characteristic of the typical individual with dyslexia). With the appropriate input, the former group could develop the brain maps of the normal reader. The cognitive and linguistic deficits of the individual with dyslexia suggest a more pervasive difficulty, which is constitutional in nature and presents a distinct therapeutic challenge.

Intervention studies have demonstrated that intensive (daily, one on one, and small group), phonologically based treatments can close the gap for reading accuracy, even in those children falling as low as the 2nd percentile in word-level reading skills. In his intervention study, Torgesen and colleagues contrasted the two treatment approaches described in the prevention study above.(1) a multisensory, bottom–up, explicit approach for developing phonemic awareness and phonemic decoding and encoding skills with minimal text instruction (the Lindamood program, described above) and (2) the embedded phonics instruction approach in which only 20% of the time was spent on single-word phonemic decoding activities and the rest on text reading and sight word training.[9,11,12] The children were 8 to 11 years old and fell in the 2nd percentile for word-level reading ability and the 10th percentile on a broad reading measure, combining word reading with comprehension (Broad Reading Score, Woodcock Johnson Tests of Achievement, Revised).[13] Intensive remediation was delivered on a one-to-one basis, 5 days a week for 100 minutes a day for 8 weeks, and the children then returned to their special education classrooms.

Figure 1 provides a snapshot of the findings. The growth of the children's reading skills in both conditions was measured on a broad measure combining word reading accuracy and passage comprehension into a single standard score (mean 100, SD 15; thus, a value from 85 to 115 is in the average range).

Treatment effects.broad reading skill measures (Woodcock Johnson Test of Achievement, Third Edition, standard score mean 100, SD ± 15) before 16 months of special education (P-Pretest), before 9 weeks of intensive remediation (Pre), immediately after 9 weeks of remediation (Post), and at 1- and 2-year follow-up. The dotted horizontal line represents the group mean IQ. EP = embedded phonics; LIPS = Lindamood Phoneme Sequencing.

For the 16 months before the intervention, the children were in special education classes, where the instruction maintained their level but did not close the gap. The intensive intervention produced a steep rate of reading growth, regardless of the intervention, and gains continued over the 2 years, with the children reaching mean standard scores above 90, approximately the 30th percentile, which was also their mean Wechsler Verbal IQ. Even the children with the lowest verbal short-term memory (standard score 70–85) as measured by the Digit Span subtest of the Wechsler Intelligence Scale for Children-Revised (WISC-R)[14] made gains in phonemic decoding similar to those of the group as a whole (mean standard score 70.2 to 93.5). At follow-up, 40% of the children had been staffed out of the special education classrooms, a considerably higher percentage than the county's record of less than 5%.

Whereas almost all of the children made significant gains during the intervention period, only a little more than half sustained or increased their gains during follow-up. Furthermore, about a fourth of the children lost most of the gains made during the intervention during the 2-year follow-up period. The variables predicting growth during the follow-up were attention, receptive language ability, and socioeconomic status. Of note, the more implicit top-down approach was as effective as the multisensory bottom-up approach, suggesting that the children could harness the phonics rules despite having weak phonologic representations. This would suggest that they now had the executive function and abstract thinking abilities to compensate.

Unfortunately, the fluency gap could not be narrowed with this intensive intervention, and the children remained severely impaired in reading rate (2nd percentile). To explore this further, Torgesen and colleagues conducted small-group intervention studies with older (11–12 years) reading-disabled children.[15] All children were severely impaired in word reading fluency (2nd percentile), but one group was mildly impaired (30th percentile) and the other moderately impaired (10th percentile) for word reading skills. The intervention used the Spell, Read Phonological Auditory Training,[16] which provided systematic instruction in phonemic awareness and phonemic decoding combined with fluency-oriented practice from the start. The mildly impaired group evidenced significant gains in both accuracy and fluency, with fluency improving from the 2nd percentile to approximately the 50th percentile after only 60 hours of treatment. The moderately impaired readers were further subdivided into two groups, which received different durations of treatment. One group received 50 hours of treatment, and the other received 100 hours. Although the gains in text reading accuracy and fluency on the Gray Oral Reading Test, Third Edition,[17] were significant in both groups, the longer instruction period produced greater gains in accuracy (19 vs 8 standard score point improvement) and fluency. The group exposed to the longer duration of treatment improved in fluency from a mean standard score of 65 to 79 (14 standard score points—nearly 1 SD), whereas the group exposed to a shorter duration of treatment showed a 9 standard score point improvement (68 to 78). Clearly, fluency remained a significant problem for both groups.

Figure 2 illustrates the results from the prevention study of the young at-risk children as well as the remediation study of the older, reading-disabled children.[15] Treatment of the young at-risk children in the prevention study resulted in normal accuracy and fluency at the end of fourth grade, emphasizing the importance of early identification and treatment.[8] Although the mildly impaired readers (30th percentile) experienced very significant growth after treatment, they still evidenced a gap between accuracy and fluency. The more severely impaired readers (10th percentile) made significant gains in accuracy but remained impaired in fluency. The longer duration of treatment in the moderately impaired readers resulted in more gains but was still inadequate. The most severely impaired (2nd percentile) readers from Torgesen et al's intervention study also made significant gains in accuracy but no gains in fluency.[11]

The fluency gap.a comparison of word-level fluency gains immediately after intensive, phonologically based treatment in groups of reading disabled (RD) children, with varying severity of difficulty prior to treatment. The two groups of RD children in the 10th percentile illustrate that longer treatment duration (Rx hrs) yielded greater gains in accuracy but no response with fluency. A contrast group of at-risk children, who had received intensive intervention through second grade, illustrates maintenance of gains through fourth grade, with normal fluency. The horizontal line represents the 30th percentile benchmark.

Torgesen and colleagues conducted a subsequent intervention study with two groups of severely impaired (2nd percentile) 9- to 11-year-old children using two interventions.(1) the Lindamood Phoneme Sequencing program[12] for 67.5 hours, followed by 67.5 hours of fluency instruction (repeated reading and word drills) and comprehension instruction, and (2) an accuracy-only group, which received only the Lindamood Phoneme Sequencing instruction, with equal time in comprehension instruction.[15] Preliminary findings based on 45 of the 60 children who finished the study reveal similar accuracy and fluency outcomes for both groups, with significant gains in accuracy but none in fluency. Neither fluency instruction nor a longer duration could close the gap.

The studies by Torgesen et al. support the need for early intervention for the development of fluent word reading. Torgesen proposed that because the acquisition of sight words occurs with repeated exposure to words in print, individuals with dyslexia do not read, and the fluency gap widens.[1] Those older children who are remediated and acquire the phonologic decoding ability for accurate reading would have to read more than other children to close the sight word gap. Other factors contributing to poor automatic word reading and text reading fluency can be child characteristics such as rapid naming, attention deficit, executive function deficits, or receptive language ability. In their 2001 study, Torgesen et al. found that attention, receptive language ability, and socioeconomic status were predictive factors in this population.[11] Indeed, the children in the 2001 study were found to have significant language impairment as measured by the Clinical Evaluation of Language Fundamentals, Third Revision,[18] with a mean total language standard score of 76.3 (+ 9.0) for the group receiving the Lindamood Phoneme Sequencing, and of 81 (+ 12) in the embedded phonics group. Interestingly, these language-impaired children showed a significant improvement in the total language standard score at 1-year follow-up.the Lindamood Phoneme Sequencing group standard score improved to 89.7 (+ 14), and the embedded phonics group standard score improved to 89.9 (+ 19.3). Both the explicit and the more implicit phonologic interventions were effective in significantly enhancing spoken language processing and written language.

Pokorni et al. reported minimal gains in language and reading-related skills in a group of 18 younger, language-impaired, poor readers, aged 7.5 to 9 years.[19] Their scores on the Clinical Evaluation of Language Fundamentals, Third Edition,[18] fell more than 1.5 SD below the mean, and they were moderately reading impaired (18–25th percentile). These children received the Lindamood Phoneme Sequencing intervention for approximately the same number of hours of daily treatment, but in a small group (four children to one instructor). Two other groups also received equal time and intensity of treatment using either Earobics Step II[20] or FastForWord,[21] computer programs designed to remediate auditory temporal processing deficits. The Lindamood Phoneme Sequencing group alone made significant gains in phonologic awareness, as well as segmenting and blending after 60 hours of intervention. However, no gains in reading were observed. This would suggest that the more intensive, one-on-one intervention is more effective, particularly for children with both oral and written language impairments. Moreover, Lindamood Phoneme Sequencing is a complex program, and considerable training is required to work effectively with very impaired children. It is possible that the training and experience of the therapists, which were not specified in this study, might not have been as extensive as reported in Torgesen et al's 2001 study,[11] and might have been a contributing factor. The authors cautioned that the study was limited by a small sample size, a heterogeneous group, and an absence of IQ scores.

In addressing the comprehensive and multidimensional needs of children with dyslexia, especially in the areas of oral (rapid naming) and reading fluency, Wolf et al. reported the preliminary findings of their longitudinal intervention study with reading-disabled children.[22] Interventions contrasted three different treatment strategies. All subjects were trained using an evidence-based phonologic treatment (Phonological Awareness and Blending/Direct Instruction, developed by Lovett et al.[23]) followed by three different protocols.(1) RAVE-O (Retrieval, Automaticity, Vocabulary Elaboration, Orthography), developed by Wolf et al. "to simultaneously address the need for automaticity in phonological, orthographic, semantic, syntactic, and morphological systems and the importance of training explicit connections between these linguistic system"[24] ; the comprehensive interventions with emphasis on the semantic aspects of language (vocabulary and retrieval) set it apart from other linguistic intervention studies; (2) Word Identification Strategy Training (teaching other strategies for analyzing words)[23] ; and (3) Teaching Classroom Survival Strategies.[22] Subjects were second- and third-graders. They received 70 sessions of small-group, daily interventions. Preliminary findings reported by Wolf et al. on the children with low average vocabulary scores revealed that the Phonological Awareness and Blending/Direct Instruction plus RAVE-O group improved more than the Phonological Awareness and Blending/Direct Instruction plus Word Identification Strategy Training group.[22] On the Gray Oral Reading Test, Third Edition, Reading Quotient (a combined measure of rate, accuracy, and comprehension subtests), the Phonological Awareness and Blending/Direct Instruction + RAVE-O group showed a 10-point standard score gain (74 to 84) compared with the Phonological Awareness and Blending/Direct Instruction plus Word Identification Strategy Training group, which showed only a 4-point standard score improvement (74 to 78). However, at the 1-year follow-up, both groups were performing similarly, in the low 80s (Lovett M, personal communication, 2004). The Phonological Awareness and Blending/Direct Instruction plus Classroom Survival Strategies group scores showed a nonsignificant decline from a standard score of 76 to a standard score of 74. The final results of this comprehensive multidimensional study should yield helpful information about the response of the children's various cognitive and linguistic characteristics, including rapid naming, to differing linguistic interventions (semantic, morphologic, orthographic) with a core phonologic component.

In summary, these phonologically driven linguistic treatment studies indicate that the younger the child, the more explicit the intervention must be; the older the child and the more severe the impairment, the more intensive the treatment, and the longer its duration must be. A systematic phonics approach results in robust results in word reading accuracy but is not effective in developing fluency in the older, more impaired reader. Further research is needed to establish more effective interventions that will enable these children to become skilled readers.

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