Barkley (1997a) proposed that the central deficit in Attention Deficit Hyperactivity Disorder (ADHD) is in behavioral inhibition, resulting in deficits both in working memory and sense of time. To test this theory, 21 children with ADHD and a matched sample (ages 6-13) completed a variety of tasks that measured behavioral inhibition, working memory, attention, and time reproduction. Children with ADHD performed significantly below controls on measures of inhibition, attention, and time reproduction. They did not differ significantly from controls, however, on tasks of working memory. In addition, performance on the working memory tasks was not correlated with the time reproduction task. We discuss the relevance of these results in the context of current theories of ADHD.