The current study sought to understand if performance on an executive functioning test was related to academic skills in children with ADHD-C. Because many children with ADHD experience executive function impairments and academic underachievement, it was hypothesized that executive functioning performance (specifically, RI) would be related to lower academic functioning.
Results suggest that typically developing children with ADHD-C with average reading, writing, spelling, and mathematical calculation skills may still score lower than matched peers on tests of RI. Moreover, nearly 25% of the ADHD-C group was impaired (% that fell at or below 1 SD
normed average) on the Color Naming and Inhibition subtests. Despite their significantly lower performance compared with controls, the ADHD-C group scored in the average range on all Color-Word Interference measures and demonstrated high-average GCA as a group. This pattern of performance is not altogether surprising given that executive function tests are less sensitive when children with ADHD possess above average intelligence (Mahone et al., 2002
Regression analyses found a statistically significant relationship between Written Expression and Inhibition performance. No other academic measure was statistically related to Inhibition performance. It is hypothesized that the cognitive demands required for writing may be more strongly related to those important for RI. For example, Written Expression requires many complex mental operations that may be influenced by RI. The ability to recall correct grammar, use appropriate sentence structure, plan, and organize a coherent paragraph, all under time constraints, is required to achieve an adequate score on Written Expression. We observed significant correlations between Color Naming and Word Reading and Written Expression, which also suggests that the ability to rapidly read and process stimuli may be important for writing ability. Recent investigations on the relative influence of executive functioning on Written Expression ability in adults with ADHD suggest an important relationship. Semrud-Clikeman and Harder (2010)
found 31% of the variance in SATA writing mechanics to be accounted for by executive functioning ability (D-KEFS Color-Word Interference, Tower, and Controlled Word Association Test). They reported a nearly significant relationship (p
= .053) between D-KEFS Interference and writing mechanics performance. While the ecological validity of executive functions is still up for debate, our results suggest the mental operations involved in writing ability may be influenced in part by one's ability to inhibit automatic responding.
It is important to note that spelling, mathematics, and reading ability did not appear to be statistically related to RI. This suggests that impairments in RI may be unrelated to some academic skills. There are many cognitive processes under the umbrella of executive functions; we only chose to study one of them. Because we did not find that RI predicted many academic skills (with the exception of Written Expression) it is suggested that other executive functions (e.g., verbal and/or spatial working memory, planning) may be better suited to explain academic deficits in those with ADHD. For example, Clark, Prior, and Kinsella (2002)
found that verbal ability was predictive of communication and reading performance in children with ADHD. Thus, research on verbal fluency and verbal working memory functioning in children with ADHD and outcomes for reading and verbal communication may illumine the executive functioning—academic achievement relationship.
Children with ADHD often experience comorbid psychiatric disorders, including learning, mood, and conduct problems. Indeed, the high rate of comorbid disorders and use of clinically referred samples from medical schools and hospitals provides important information for this group of children with ADHD but does not speak to the majority of those with ADHD who do not experience psychiatric comorbidity or receive treatment through major medical schools or hospitals. For this reason, the current study was unique in that it included typically developing children with ADHD-C. Our results suggest that there may be important differences between clinically referred and typically developing (e.g., not clinically referred for treatment) children with ADHD-C.
Future work should take into account the natural variation with respect to social, emotional, psychological, academic, and biological differences in individuals with ADHD-C. It is important to attain relatively large numbers of research participants in order to achieve statistical power; however, researchers should consider that including heterogeneous samples in favor of statistical power may increase the likelihood of Type 2 errors. Theory-driven research with clearly defined and homogenous ADHD groups may yield important information about the potential neuropsychologically impaired subgroups (Nigg, Willcutt, Doyle, & Songua-Barke, 2005
) under the ADHD umbrella.
Our study had limitations that may limit the generalizability of the findings. RI is a complex cognitive process that is difficult to define. Nonetheless, we defined the cognitive process of RI as one's standardized score on the D-KEFS Inhibition test. Others have used go/no go tasks as outcome measures for RI and found significant difficulties in children with ADHD (Wodka et al., 2007
).The use of different tests and therefore different definitions of neuropsychological processes are a good way of testing theoretically driven hypotheses about the relationship between executive functions and ADHD. Our sample size (40 ADHD and 20 Control) was relatively small yet provided adequate statistical power to detect the effect sizes of interest. While it is difficult to garner large, relatively homogenous samples of children with ADHD, larger sample sizes will provide more externally valid research findings. Our sample was also restricted to those with ADHD-C and did not include children with other ADHD subtypes. Because research suggests that there may be differences between those with ADHD-C and ADHD-PI (Wodka et al., 2008
), future work should continue the search for subtype differences. Follow-up studies that include children with ADHD-PI and
ADHD-C might provide interesting findings regarding potential differences with regard to the potential mediating effects of executive functions on real-world abilities.