This trial is a continuation of the Multimodal Treatment Study of Children with Attention Deficit Hyperactivity Disorder (MTA Study). Continuation Aim 1 is to track the persistence of intervention-related effects as the MTA sample matures into mid-adolescence, including subsequent mental-health and school-related service utilization patterns as a function of MTA treatment experience (treatment assignment) and outcome (degree of treatment success at 14 mo.). Aim 2 is to test specific hypotheses about predictors, mediators, and moderators of long-term outcome among children with ADHD (e.g., comorbidity; family functioning; cognitive skills; peer relations) that may influence adolescent functioning (either independent of or through initial treatment assignment and/or 14-month treatment outcomes); and to compare how these predictors, mediators, and moderators are similar or dissimilar within the normal comparison group. Aim 3 is to track the patterns of risk and protective factors (including their mediation or moderation by initial treatment assignment and/or outcome) involved in early and subsequent stages of developing substance-related disorders and antisocial behavior. Aim 4 is to examine the effect of initial treatment assignment and degree of treatment success on later academic performance, achievement, school conduct, tendency to drop out, and other adverse school outcomes.