Working Memory, Processing Speed, and Academic Achievement in Adults with ADHD

In Barkley’s (1997a, 1997b) model of attention-deficit/hyperactivity disorder (ADHD), he proposes that working memory deficits resulting from ADHD may cause impairments in reading comprehension. ADHD has been associated with poorer processing speed and working memory as well as academic underachievement in some studies. However, more research is needed examining the relationship between ADHD, working memory, processing speed, and academic achievement in adults to help elucidate the neuropsychological correlates of ADHD and their potential impact on academic functioning. The aim of the current study is to examine the relationship between ADHD, verbal working memory performance, processing speed, and academic achievement in adults as well as to investigate the academic achievement performance of potential subtypes of adult ADHD characterized by working memory deficits or processing speed deficits. Adult participants with and without ADHD were administered measures of verbal working memory and processing speed from the Wechsler Adult Intelligence Scale-Third Edition, as well as academic achievement measures from the Woodcock-Johnson Third Edition Tests of Achievement. The performance of adults with ADHD and controls were compared on measures of verbal working memory, processing speed, and academic achievement. Processing speed was also investigated as a potential mediator of ADHD status and academic achievement scores. Additionally, the academic achievement scores of ADHD adults with processing speed or verbal working memory deficits were compared to ADHD adults without those specific neuropsychological deficits as well as controls with and without those specific neuropsychological deficits. ADHD was associated with poorer performance on processing speed and academic fluency measures. However, ADHD and control groups did not differ in their performance on verbal working memory composites or untimed measures of academic achievement. Processing speed was found to mediate the relationship between ADHD and academic fluency, and processing speed and working memory deficits were associated with poorer academic achievement performance in adults with ADHD and controls. These results are consistent with a view of ADHD as a heterogeneous condition with poorer processing speed being present in at least a subgroup of adults with ADHD and accounting in part for the relationship between ADHD and academic fluency