Theories of attention deficit/hyperactivity disorder (ADHD) increasingly highlight the role of neuropsychological impairment in ADHD; however, a consistent and identifiable pattern of performance on tests is not well established. The National Institutes of Health (NIH) Executive Abilities: Measures and Instruments for Neurobehavioral Evaluation and Research (EXAMINER) battery provides measures of common variance across multiple executive function tests within specific domains and was used to characterize which executive functions are most affected in children with ADHD. Thirty-two children (24 male), ages 8–15 years (M = 12.02; SD = 2.29), diagnosed with ADHD and no comorbid disorder completed the NIH EXAMINER battery. Sixty age and gender matched healthy controls were chosen from a database of participants enrolled in the NIH EXAMINER multi-site study. Children with ADHD performed worse on the working memory score compared with the controls. No differences were found on the cognitive control or fluency scores. For children with ADHD, poorer working memory performance predicted parent report of child learning problems. Cognitive control and fluency scores did not predict learning problems. In summary, working memory emerges as a primary impairment in children with ADHD who have no comorbid disorders. Furthermore, working memory weaknesses may underlie the academic problems often seen in children with ADHD. (JINS, 2013, 19, 1–11)