Attention, memory, executive function, language, and visual-motor skills were evaluated in a sample of 621 children, 6 to 11 years old, to assess the discriminant validity of neuropsychologic testing. Attention deficit hyperactivity disorder cases (249) and controls (372) were identified and tested. Analysis of covariance, nonparametric comparison tests, effect sizes, discriminant function, factor analyses, and receiver-operator characteristics curve analyses were used to establish the best diagnostic cutoff points for each variable. Statistically significant differences were found on cognitive effort, auditory skills, continuous performance test, working memory, visual-motor skills, verbal comprehension, and executive function measures (P < 0.05); however, the effect of group sizes was low to modest (0.24 to 0.54). Receiver-operator characteristics curve analysis showed modest sensitivity and low specificity, demonstrating that an important proportion of the variance in test scores was overlapping. Factor analysis of neuropsychologic testing results revealed a structure of six factors each for attention deficit hyperactivity disorder, control, and combined samples. The latent variables produced one discriminant function with a total correct classification accuracy of 61.9%. Neuropsychologic tests should be used as Attention Deficit Hyperactivity Disorder diagnostic tools with caution, but they hold promise for identifying core cognitive deficits and processes that can aid prevention and intervention.