ADHD and reading disabilities: a cluster analytic approach for distinguishing subgroups

Data suggest that children with reading disability (RD) and non-RD children with attention-deficit/hyperactivity disorder (ADHD) may comprise distinct subgroups. Research has been hampered by variance in definitional criteria, which results in the study of different subgroups of children. Using cluster analysis, this study empirically divided children with ADHD (N = 54), based on their Full Scale IQ (FSIQ) and reading ability. Four distinct subgroups emerged in which cognitive, behavioral, and neurochemical function was compared. Cluster 1 was of average FSIQ and reading scores; Cluster 2 was of average FSIQ but showed impairment in reading; Cluster 3 had high FSIQ and reading scores; and Cluster 4 had low scores in both domains. The groups had different patterns of cognitive, behavioral, and neurochemical function, as determined by discrepancies in Verbal-Performance IQ, academic achievement scores, parent aggression ratings, and a measure of noradrenergic function. These distinctions are discussed with regard to etiology, treatment, and long-term outcome.     

The relationship between IQ and reading disabilities in English-speaking Canadian and Spanish children

This study was designed to examine the role of intelligence (IQ) in the definition of reading disabilities (RD) in languages with different orthographic systems. A sample of 94 Spanish children and 157 English-speaking Canadian children with RD was classified into four groups on the basis of IQ scores from the Wechsler Intelligence Scale for Children-Revised (< 80; 81-90; 91-109; 110-140). We examined the reading and spelling skills of Canadian and Spanish children as a function of Full Scale, Verbal, and Performance IQ scores. Significant differences between the languages were found when reading performance was analyzed as a function of Verbal IQ scores, in that there were some differences between the groups of Canadian children with RD but not between the groups of Spanish children. The Canadian children with Verbal IQ scores < 80 demonstrated relatively lower performance in reading and spelling skills than the Canadian groups with higher IQ scores. There were differences in reading tasks as a function of Performance IQ in English but not in Spanish. The differences in the role of IQ as a function of orthographic systems may relate to the greater significance of visual-orthographic as opposed to phonological processing in English.     

Longitudinal Study of Reading Disability and Attention-Deficit/Hyperactivity Disorder: Implications for Education

ABSTRACT— The majority of children who receive special education services meet criteria for reading disability (RD) or attention-deficit/hyperactivity disorder (ADHD), but additional research is needed to understand the long-term academic outcome of children in these groups. Individuals with RD only ( N = 71), ADHD only ( N = 66), both RD and ADHD ( N = 51), or neither disorder ( N = 118) were identified through the ongoing Colorado Learning Disabilities Research Center twin study and retested 5 years later. Results of the follow-up testing indicated that, in addition to ongoing reading difficulties, individuals with RD exhibited higher rates of academic difficulties, depression, and adolescent-onset conduct disorder. Initial ADHD status was associated with academic and social difficulties and elevated rates of nearly all comorbid disorders 5 years later. The group with comorbid RD and ADHD had more stable reading deficits than the group with RD without ADHD and exhibited greater impairment than groups with either disorder alone on outcome measures of academic functioning and social difficulties. These results suggest that individuals with both RD and ADHD are at increased risk for negative outcomes as adolescents and young adults and that when RD and ADHD co-occur, interventions should be provided for both disorders.     

Motor correlates of ADHD: contribution of reading disability and oppositional defiant disorder

This study investigated whether the likelihood of motor impairment in children with attention-deficit/hyperactivity disorder (ADHD) increases with the presence of other disorders, and whether the co-occurring diagnoses of reading disability (RD) and oppositional defiant disorder (ODD) account for the motor deficits seen in ADHD. A total of 291 children (218 boys, 73 girls) participated. Six groups of children were compared: ADHD only (n = 29); RD only (n = 63); ADHD and RD (n = 47); ADHD and ODD (n = 19); ADHD, RD, and ODD (n = 21); and typically developing control children (n = 112). Motor skills were assessed with the Bruininks-Oseretsky Test of Motor Proficiency and the Beery Test of Visual-Motor Integration. We found that the motor skills of the ADHD-only group did not differ from the typical control group. Furthermore, motor impairment in ADHD increased as a function of co-occurring disorders, and the presence of RD rather than ADHD predicted motor impairment.     

EEG analysis of children with attention-deficit/hyperactivity disorder and comorbid reading disabilities

This study investigated electroencephalographic differences between two groups of children with attention-deficit/hyperactivity disorder, combined type, with reading disabilities (ADHD + RD) or without (ADHD) and typical control participants. Twenty participants were included in each group. All participants were between the ages of 8 and 12 years, and groups were matched on age and gender. The electroencephalographic (EEG) was recorded during an eyes-closed resting condition from 21 monopolar derivations, which were clustered into nine regions for analysis. The EEGs were Fourier-transformed to provide absolute and relative power estimates for the delta, theta, alpha, and beta bands. Ratio coefficients were also calculated for the theta/alpha and theta/beta ratios. Compared with controls, the clinical groups demonstrated the increased slow-wave and reduced fast-wave activity commonly reported in the ADHD literature. The ADHD + RD group had more relative theta, less relative alpha, and a higher theta/alpha ratio than the ADHD group. A number of hemispheric differences were also found in the delta and alpha bands. These results suggested that some of the EEG divergences found in the ADHD + RD group represent an electrophysiological component associated with the reading disability that is independent of the EEG divergences found in ADHD.     

Reading motivational differences among groups: Reading disability (RD), attention deficit hyperactivity disorder (ADHD), RD + ADHD,and typical comparison

This study assessed the reading motivation of 133 students at individual grade levels (2nd–5th), who were divided in subgroups with and without reading disabilities/difficulties (RD) and with and without attention deficit hyperactivity disorder (ADHD). Major findings were that students in the RD subgroup had lower reading motivation (intrinsic, extrinsic, and self-efficacy) and read less for enjoyment than the nondisability (ND) group; students in the combined group (ADHD + RD) showed these motivational deficits in earlier grade levels. However, students with ADHD did not differ from the ND group in reading motivation, and children with RD (with and without ADHD) were equivalent to ND in social motivation up to the 5th grade. Implications of these findings were (a) social reading is an instructional pathway for both groups of students with RD, (b) assessments of reading motivation, in addition to reading skill, may be important in assessing responses to intervention, and (c) motivational interventions should be implemented early before motivational responses become a motivational style.     

Stability of WISC-R scores in children with learning difficulties

Student records of 130 children with learning difficulties who had been tested twice were examined to determine the stability of WISC-R scores over time. There were significant losses in Verbal IQ and Full Scale IQ. Subjects in the above-average IQ range had greater losses in Verbal IQ and Full Scale IQ and greater gains in Performance IQ than did those in the below-average IQ range. Children initially tested before age 8 had a significant IQ loss, but those tested after age 8 maintained a constant IQ. The WISC-R is most frequently administered to children with learning difficulties. Results presented here suggest that the IQs in this population are not as stable as was previously thought, and this may provide a rationale for the periodic readministration of the WISC-R.     

The relative roles of IQ and cognitive processes in reading disability

The purpose of the present study was to explore the relative roles of IQ and cognitive processes in reading performance. A sample of 443 Spanish children (264 male, 179 female) ranging in age from 7 to 13 years were classified into four groups according to IQ scores (<80, 80–90, 90–110, >110) and reading disabled (RD) and normally achieving readers (NR) were compared. The findings indicate that IQ scores were not related to the differences between children with RD and NR. We found that reading‐related cognitive deficits do differentiate between RD and NR children. Therefore, IQ scores do not make a significant contribution to our understanding of reading disability.     

Reading difficulties and attention‐deficit/hyperactivity behaviours: evidence of an early association in a nonclinical sample

Attention‐deficit/hyperactivity disorder (ADHD) often co‐occurs with reading disability. A cross‐sectional study in an Italian‐speaking, nonclinical sample was conducted in an attempt to document the existence of an early association between reading difficulties (RD) and ADHD behaviours. We recruited a sample of 369 children in their first year at primary school. Of the sample, 8.4% displayed RD; 7.0% had ADHD; 3.5% presented both RD and ADHD behaviours; 50% of the children with ADHD displayed RD; 41.9% of those with RD displayed ADHD behaviours. Low socioeconomic status was associated with a fourfold increased probability of displaying RD (odds ratio = 3.98), but not ADHD behaviours. In this nonclinical sample, we detected an early association between ADHD behaviours and RD. A key role in this association may be played by inattention symptoms, which occurred with significantly increased frequency also in the group presenting only RD.     

Cognitive functioning as measured by the WISC-R: do children with learning disabilities have distinctive patterns of performance?

Patterns of performance on the Wechsler Intelligence Scale for Children-Revised (WISC-R) have been proposed as useful tools for the identification of children with learning disabilities (LD). However, most of the studies of WISC-R patterns in children with LD have been plagued by the lack of a typically achieving comparison group, by failure to measure individual patterns, and by the lack of a precise definition of LD. In an attempt to address these flaws and to assess the presence of patterns of performance on the WISC-R, we examined data from 121 children with typical achievement (TA), 143 children with reading disabilities (RD), and 100 children with a specific arithmetic disability (AD), ages 6 to 16 years. The results indicated that the RD and AD groups had significantly lower scores than the TA group on all the Verbal IQ subtests. Many of the children with AD and RD showed a significant difference between Verbal and Performance IQ scores, but so did many of the typically achieving children. Although there were some children with LD who showed the predicted patterns, typically, 65% or more of the children with LD did not. Furthermore, a proportion of the TA group-generally not significantly smaller than that of the RD and AD groups-showed discrepancy patterns as well. Our results indicate that the patterns of performance on intelligence tests are not reliable enough for the diagnosis of LD in individual children. Therefore, it might be more profitable to base the detection of an individual's LD on patterns of achievement test scores.     

A Four Year Follow‐up Study of Low Socioeconomic Status,Latin American Children with Reading Difficulties

This paper presents the results of a follow‐up study of reading difficulties among Spanish‐speaking Latin American children of low socioeconomic background (SES) over four school years. The research started with a group of 93 children with reading difficulties (RD) by 2nd and 3rd grade teachers in four schools and a control group of 63 children without reading difficulties (ND), belonging to the same schools. Both groups were equivalent in age, grade, gender and SES. All children were tested on reading decoding and comprehension, reading and writing pseudo‐words, verbal abilities, visual perception, phonological processing, and the WISC‐R. Neither SES nor IQ accounted significantly for the reading difficulties in the RD group. The most predictive variables of the final reading level in the RD group were phonological processing, verbal abilities, and the initial level of decoding. After four years, 17% of the initial RD children had reached an average level of reading, but 11% of this group remained with severe reading difficulties and may be considered as dyslexic children. The RD children who became average readers were not significantly different from the control group in verbal abilities, nor in phonological processing. Nevertheless, they were significantly different in terms of IQ scores. The neuropsychological characteristics of the children with severe reading difficulties appear similar to those found in children with dyslexia in more developed countries.     

Boys with reading disabilities and/or ADHD: distinctions in early childhood

We examined distinctions in the early childhood characteristics of boys with reading disabilities (RD) and/or attention-deficit/ hyperactivity disorder (ADHD). A four-group mixed design consisting of boys identified at age 11 with reading disabilities only (RD only; n = 46), reading disabilities and ADHD (RD/ADHD; n = 16), ADHD only (n = 20), and a comparison group (n = 281) was utilized. Differences on receptive and expressive language and temperament for ages 3 and 5 were investigated. Analyses indicated that the boys from the RD-only group performed worse on measures of receptive and expressive language. The results also indicated that boys from the RD/ADHD groups consistently performed worse on measures of receptive language and exhibited more behaviors indicative of an undercontrolled temperament. In summary, we suggest that reading disabilities and ADHD represent moderately unique disorders that frequently co-occur and are characterized by distinct developmental pathways.     

Clinical importance of parent ratings of everyday cognitive abilities in children with learning and attention problems

This study addressed two issues: first, whether parental reports contribute information over and above a standardized psychometric assessment, and second, whether parental reports of everyday cognitive functioning might be useful in distinguishing between children with reading disabilities (RD), attention-deficit/hyperactivity disorder (ADHD), and combined ADHD + RD. Parent-reported information on 159 children with learning or attention problems was obtained using a questionnaire called the Parent Ratings of Everyday Cognitive and Academic Abilities (PRECAA). Psychometric information used for comparison included the Woodcock-Johnson Psychoeducational Battery-Revised, the Bruininks-Oseretsky Test of Motor Proficiency-Short Form, the Vocabulary and Block Design subtests of the Wechsler Intelligence Scale for Children, 3rd edition, and the Developmental Test of Visual-Motor Integration. The PRECAA was found to be sensitive to group differences between children with RD and children with ADHD and combined ADHD + RD. Its inclusion resulted in a significant increase in the number of children correctly classified compared to the use of psychometric measures alone. The PRECAA correctly classified more children (66%) than did the standard psychometric measures (50%). In fact, a very high percentage of children with ADHD (81%) were correctly classified using the PRECAA. These findings suggest that the PRECAA may be a useful aid to clinicians in the identification of children with learning and attention problems.     

Information processing deficits in children with attention-deficit/hyperactivity disorder, inattentive type, and children with reading disability

We examined the information processing capabilities of children diagnosed with the inattentive subtype of attention-deficit/hyperactivity disorder (ADHD) who had been characterized as having a sluggish cognitive tempo. Children referred for school-related problems (n = 81) and nonreferred community controls (n = 149) participated. Of the referred children, 24 met criteria for ADHD, 42 met criteria for reading disability (RD), and 9 of these were comorbid for RD and ADHD. Children with ADHD differed from those without ADHD on a visual search task but not on an auditory processing task; the reverse was true for children with RD. Decomposition of the visual search task into component operations demonstrated that children in the ADHD group had a slow processing rate that was not attributable to inattention. The children with ADHD were not globally poor at information processing or inattentive, but they demonstrated diminished speed of visual processing.     

Cognitive profiling in Chinese developmental dyslexia with attention-deficit/hyperactivity disorders

The cognitive profiles of children with Developmental Reading Disorder (RD) and Attention-Deficit/Hyperactivity Disorders (ADHD) have been extensively studied in alphabetic language communities. Deficits in phonological processing and rapid naming have been implicated as core features of RD although whether the latter is a deficit specific to RD remains controversial. Similar research aiming to explore the cognitive profiles of children with both RD and ADHD in non-alphabetic language communities is limited. The specificity of rapid naming deficit to RD among Chinese has yet to be studied. In the first study, 43 Chinese children with confirmed diagnoses of RD + ADHD were assessed on their cognitive abilities in relating to reading. In the second study, the specificity deficit hypothesis of rapid naming to RD but not ADHD was examined. A digit naming test was administered to the RD + ADHD group (43 subjects) and an ADHD only group (49 subjects). In regard to cognitive profiling, rapid naming and orthographic knowledge were found to be the most common deficits among the Chinese RD + ADHD group. This co-morbid group was also found to have a significant deficit performance on the rapid naming task than the ADHD only group. The present findings support the double dissociation hypothesis in cognitive deficit between RD and ADHD. The results of both studies are discussed with reference to the findings of the Western counterparts.     

Relationship between PPVT and WISC-R in children with reading disabilities

The Peabody Picture Vocabulary Test (PPVT), Form A was compared to the Wechsler Intelligence Scale for Children-Revised (WISC-R) in two samples of children with reading disabilities. One group of 14 children, referred to a university clinic, were administered the WISC-R, followed by the PPVT. The second group of 38 children from a private learning disability center were administered the PPVT first, followed by the WISC-R. In the combined sample, the PPVT IQ (X̄ = 109.2) was significantly higher than the WISC-R Verbal IQ (X̄ = 98.9), Performance IQ (X̄ = 97.0), and Full Scale IQ (X̄ = 97.5). Similarly, the PPVT IQ was significantly higher than the WISC-R Full Scale in both samples separately, regardless of which test was administered first. In one case, the PPVT IQ was 50 points higher than the WISC-R IQ. Correlations between the PPVT and WISC-R Verbal, Performance, and Full Scale IQs were significant (rs = .56, .29, and .50, respectively). The results suggest that the two tests do not provide interchangeable IQs for a population of reading disabled children.     

Do the effects of computer-assisted practice differ for children with reading disabilities with and without IQ-achievement discrepancy?

This study was designed to assess whether the effects of computer-assisted practice on visual word recognition differed for children with reading disabilities (RD) with or without aptitude-achievement discrepancy. A sample of 73 Spanish children with low reading performance was selected using the discrepancy method, based on a standard score comparison (i.e., the difference between IQ and achievement standard scores). The sample was classified into three groups: (1) a group of 14 children with dyslexia (age M = 103.85 months; SD = 8.45) who received computer-based reading practice; (2) a group of 31 "garden-variety" (GV) poor readers (age M = 107.06 months; SD = 6.75) who received the same type of instruction; and (3) a group of 28 children with low reading performance (age M = 103.33 months; SD = 9.04) who did not receive computer-assisted practice. Children were pre- and posttested in word recognition, reading comprehension, phonological awareness, and visual and phonological tasks. The results indicated that both computer-assisted intervention groups showed improved word recognition compared to the control group. Nevertheless, children with dyslexia had more difficulties than GV poor readers during computer-based word reading under conditions that required extensive phonological computation, because their performance was more affected by low-frequency words and long words. In conclusion, we did not find empirical evidence in favor of the IQ-achievement discrepancy definition of reading disability, because IQ did not differentially predict treatment outcomes.     

IQ and neuropsychological predictors of academic achievement

Word reading and math computation scores were predicted from Wechsler Abbreviated Scale of Intelligence Full Scale IQ, 10 neuropsychological tests, and parent attention deficit hyperactivity disorder (ADHD) ratings in 214 general population elementary school children. IQ was the best single predictor of achievement. In addition, Digit Span contributed significantly to reading prediction, and the Developmental Test of Visual-Motor Integration (VMI) and Coding contributed to math prediction. The remaining neuropsychological test scores did not significantly improve achievement prediction. Exploratory factor analysis yielded a general ability factor (comprising the four IQ subtests, Digit Span, VMI, reading, and math), five factors made up solely of subtests from single measures (Wisconsin Card Sorting Test, Stroop Color and Word Test, Gordon Diagnostic System, California Verbal Learning Test, and ADHD ratings), a factor consisting of Grooved Pegboard Test and Coding, and a factor consisting of Symbol Search and Animal Naming Test.     

Differences between WISC‐R and WISC‐III performance scale among children with ADHD

Reviews involving the Wechsler Scales for children suggest that Full Scale IQ scores on the Wechsler Intelligence Scale for Children, Third Edition, average 5 to 6 points lower than scores on the second edition of the scale [WISC‐R, Wechsler, D. (1974). Zimmerman & Woo‐Sam, 1997], with the differences distributed disproportionately over subtests, i.e., with larger discrepancies found within the Performance Scale (Wechsler, 1991). Changes on the revised subtests of the WISC‐III Performance Scale may place children with ADHD at a disadvantage compared to their performance on analogous WISC‐R subtests. We examined IQ test performance in 122 unmedicated children with ADHD (61 given the WISC‐R, 61 given the WISC‐III), and 46 children from a healthy, comparison group (23 given the WISC‐R, 23 given the WISC‐III). The ADHD and comparison group samples were matched for sex and for Verbal IQ between WISC‐R and WISC‐III. Children with ADHD had significantly lower Performance IQ on WISC‐III compared to the WISC‐R, with the Picture Arrangement subtest showing the most significant difference. In contrast, there were no significant differences between the WISC‐R and WISC‐III cohorts on Performance IQ or any Performance subtests among the comparison group. These findings highlight the importance of examining the comparability of ability test revisions among clinical and non‐clinical populations, and will be especially salient when the WISC‐III is revised. © 2003 Wiley Periodicals, Inc. Psychol Schs 40: 331–340, 2003.     

Sound links in reading and spelling with discrepancy-defined dyslexics and children with moderate learning difficulties

This study reports the effects of a highly structuredindividually administered remedial teaching programmefor children with reading difficulties. Thephonological awareness, reading accuracy and spellingattainments of 28 children diagnosed as having low IQ(Mean IQ = 66, SD = 5.3) were compared with those of29 children diagnosed as having discrepancy defineddyslexia (Mean IQ = 95, SD = 8.4). The responsivenessto intervention of each group was also compared withteacher-referred reading-delayed children matched forinitial literacy skills. For reading accuracy andphonological awareness the dyslexic group respondedmore successfully than the low IQ group. The twogroups did not differ significantly on spelling. It isargued that the reading accuracy and phonologicalawareness results are in keeping with thephonological-core variable-difference (Stanovich &Siegel 1994) model of reading disability and that thegains of all groups on all measures were such thatthere is no obvious benefit in using IQ to selectchildren for a programme of individual teaching whichcombines reading with phonological awarenesstraining.