Update on ADHD and Specific Learning Disabilities

Update on ADHD and Specific Learning Disabilities

Sam Goldstein, Ph.D.
September, 2005
Copyright © 2005

In 1994, Drs. George DuPaul and Gary Stoner reviewed seventeen studies attempting to determine the percentage of children with Attention Deficit Hyperactivity Disorder (ADHD) also experiencing any type of specific learning disability (SLD). Averaging across studies approximately one out of every three children with ADHD was found to have SLD. This is much higher than the prevalence of SLD among non-ADHD control subjects in these studies which averaged approximately 20%. Yet when these studies are examined individually, the overlap of ADHD and SLD varied significantly from a low of 18% in some studies to a high of 36% in others. Differences in these percentages are likely due to differences in the criteria used to define SLD. Higher incidence is found when briefer measures (e.g., a simple cutoff questionnaire) are used then when more stringent criteria are applied. Some researchers have argued that the overlap in adverse outcome for ADHD and SLD (e.g., reading ability, math skills, etc.) may be due to different processes. Children with ADHD struggle because of their inefficiency and lack of sustained effort ultimately falling behind their peers and eventually meeting typical discrepancy criteria for SLD used in the schools, while children with SLD absent ADHD often fall behind because they lack basic neuropsychological processes necessary to keep pace with the achievement of their peers. Thus, children with ADHD appear to know what to do but go about doing it inconsistently leading ultimately to achievement problems, while children with SLD simply don't know what to do.

When learning is considered a function of acquisition, consolidation, storage and retrieval, children with ADHD appear to possess deficits in the process of acquisition due to their inefficient use of proactive strategies when engaged in learning tasks. Their performance is inconsistent from trial to trial on verbal and visual tasks. They have poor recall because their approach to tasks is disorganized. Their memory system may be overloaded with bits of information that are not encoded within an orderly frame of reference. This phenomena may explain why so many children with ADHD absent SLD appear to know a subject the night before a test but perform poorly within the demanding framework of timed recall.

This phenomena has led Dr. Martha Denckla to suggest this theory as an explanation why children without SLD but struggling with ADHD tend to be good incidental learners but poor academic learners. They effortlessly and non-strategically acquire, consolidate, store and retrieve whatever happens to be experienced naturally. Their natural phonological and general language skills are normal. They may effortlessly learn to read more or less the way most children learn to talk. However, they may underachieve on a daily basis and experience academic deterioration as they move into the greater demands of advanced grades through the lack of planning and organizational processes. These hypothetical constructs have led many researchers to conclude that ADHD is a major source of additional and separate cognitive problems for children already struggling with SLD. It is also accepted that the language based problems experienced by many children with SLD often fuel complaints of inattention.

The volume of studies and complexity of the relationship between ADHD and SLD precludes an indepth review of even current research. In this month's article I will review a number of relevant articles highlighting important issues concerning ADHD and SLD. The volume of studies and complexity of the relationship between ADHD and SLD prevents an indepth review of current research. The studies I have chosen highlight five important issues which I will discuss at the close of the article.

Aaron, P.G., Joshi, R.M., Palmer, H., et al. (2002). Separating genuine cases of reading disability from reading deficits caused by predominantly inattentive ADHD behavior. Journal of Learning Disabilities, 35, 425-435.

These authors tested a diagnostic procedure using intra-individual differences seen in the performance of at-risk learners on tasks related to reading, that vary in their sensitivity to sustained attention required for successful performance. The authors hypothesized that children with inconsistent attention would perform more poorly on tests that require sustained attention such as listening comprehension than on tests that are more tolerant of inattention such as reading comprehension. They hypothesized that these differences would not be seen in the test scores of children with only reading disability because their performance is determined more by the difficulty level of the reading tests than by the degree of sensitivity of the task to attention. The authors collected data from thirty-nine children at risk for reading disability as identified by classroom teachers. A battery of diagnostic tests were administered. Seventeen children met the Inattentive criteria for ADHD. Sixteen met the criteria for reading disability and six met the criteria for both. The data supported the authors' hypotheses, including a finding that in spite of average reading comprehension, the listening comprehension scores of the Inattentive group with ADHD fell close to the below average range.

Adams, J. W., & Snowling, M.J. (2001). Executive function and reading impairments in children reported by their teachers as hyperactive. British Journal of Developmental Psychology, 19, 293-306.

Twenty-one 8 to 11 year olds were identified by teachers as hyperactive. In comparison to a control group, significant group differences were found on literacy measures, tasks of inhibition and executive function, but not verbal working memory measures. The authors report that their results are consistent with the hypothesis that children with hyperactivity have difficulty with behavioral inhibition. The authors propose their data supports that the core cognitive deficit in executive function associated with hyperactivity in children is independent of the phonological deficits associated with reading impairment.

Biederman, J., Mick, E., Faraone, S.V., Braaten, E., et al. (2002). Influence of gender on Attention Deficit Hyperactivity Disorder in children referred to a psychiatric clinic. American Journal of Psychiatry, 159, 36-42.

It has been suggested anecdotally and from a research basis that males are over-represented in referral for ADHD and SLD in both clinic referred and community samples. It is possible the differences in the phenotypic expression ADHD and/or severity of symptoms between males and females may be responsible for this discrepancy. In a large group of clinically referred children, these authors predicted that females would demonstrate less disruptive behavior, higher presentation of inattentive type diagnosis (ADHD-IN) and less SLD than males. However, the authors also hypothesized that when compared to same-sex controls, the impact of ADHD was predicted to be the same across gender. The authors examined 140 clinic referred females and 140 males with ADHD as well as two gender specific control groups. Structured interviews and parent reports were utilized. Within the ADHD population, girls were 2.2 times more likely to be diagnosed as ADHD-IN as boys. Girls with ADHD exhibited less disruptive behavior and less incidence of SLD than boys. However, a lack of gender by ADHD interaction in these areas indicates that the differences can be attributed to the lower overall base rate of disruptive behavior and SLD in girls. The only significant interaction concerned substance use with ADHD presenting as a more significant risk factor in girls than boys. The authors conclude that ADHD increases the risk of negative outcome and behavioral problems regardless of gender. However, the lower rate of SLD, disruptive behavior and social dysfunction for girls with ADHD versus boys may cause their impairments to be less noticeable, contributing to under-referral.

Bonafina, M.A., Newcorn, J.H., McKay, K.E., et al. (2000). ADHD and reading disabilities: A cluster analytic approach for distinguishing subgroups. Journal of Learning Disabilities, 33, 297-307.

These authors utilized a cluster analysis study of 54 children with ADHD. Children were divided based upon full scale I.Q. and reading disability into four distinct subgroups in which cognitive, behavioral and neurochemical functioning were compared. Group one possessed average full scale I.Q. and reading skills; group two possessed average full scale I.Q. but impairment in reading; group three possessed high full scale I.Q. and reading scores and group four had low scores in both of those areas. The groups had different patterns of cognitive, behavioral and neurochemical functioning as determined by discrepancies in verbal-performance I.Q., academic achievement scores, parent aggression ratings and a measure of the neurotransmitter noradrenaline. All four groups appeared consistent with a diagnosis of ADHD in that the children were rated as highly inattentive and hyperactive by their parents and teachers. They did not differ significantly on any rating of ADHD symptoms. Group one appears to represent ADHD in a pure form. In contrast group two resembled characteristics of the reading disabled group. These children tended to have less behavioral disturbance than the other groups. From a cognitive perspective, children in group three demonstrated some similarities to children referred to as experiencing a non-verbal learning disability. However, their arithmetic and performance I.Q. scores were in the normal range. Finally, group four, despite a profile similar to that of group two with regards to I.Q. academic achievement discrepancy but was considerably lower functioning overall.

Cutting, L.E., Koth, C.W., Mahone, M., & Denckla, M.B. (2003). Evidence for unexpected weaknesses in learning in children with ADHD without reading disabilities. Journal of Learning Disabilities, 36, 259-269.

These authors examined the mechanisms underlying verbal learning in children with and without ADHD, none of whom had reading disabilities. Children with ADHD were compared to typically developing children on a verbal learning test. Children with ADHD initially learned the same number of words as controls but demonstrated weaknesses recalling words after delay, suggesting they were less efficient learners. Regardless of ADHD status, males and females performed differently. Males used semantic clustering less frequently and recalled fewer words from the middle region of the list than females. Females also outperformed males in terms of overall performance despite lower verbal I.Q. scores.

1. The symptom problems of ADHD cause impairment in achievement differently than SLD, even when certain outcome measures such as reading grade level appear similar for both diagnostic groups.
2. The executive function deficits children with ADHD experience leads them to be inconsistent and inefficient learners, a pattern very different from those with SLD.
3. ADHD and SLD are separate but related phenomena. The primary neuropsychological impairments and executive process problems are different for these two conditions yet are not completely independent.
4. Additional neuropsychological phenomena such as traditionally measured I.Q. may also play a role in determining differences in the presentation and academic achievement of children with ADHD and SLD.
5. The differences observed in SLD and ADHD between genders is likely not an artifact of measurement but rather reflects true differences between the genders.

Experienced educators often attest to the dramatically increased level of impairment children with combinations of ADHD and SLD experience in school relative to either condition alone. There is clearly a need to continue researching the relationship between these two conditions. In particular it will be important to develop researched demonstrated methods of assessment and treatment for children with combined ADHD and SLD. As the school year begins, I urge educators, mental health professionals and even parents to consider the significant challenges children with combined ADHD and SLD experience, not only in school but in all important areas of their lives.