Objective: Scholastic achievement in a nonclinical sample of ADHD children and adolescents was evaluated taking into consideration variables such as comorbid learning disorders, family income, and parental education which may also be associated with poor academic performance. Method: After screening for ADHD in 396 students, the authors compared academic performance of 26 ADHD individuals and 31 controls paired for gender, age, and intelligence level considering both mathematics and Portuguese language scores. Learning disorders were investigated and the "Diagnostic and Statistical Manual of Mental Disorders" (4th ed.; "DSM-IV" ) criteria were met using structured interviews. Results: The prevalence of academic underachievement was 2.98 times higher in students with ADHD, the most frequent subtype being predominantly inattentive. Parental educational level, family income, and comorbid learning disorders could not explain the discrepancies between ADHD students and controls. Conclusions: ADHD seems to be associated with poor academic performance even in the absence of comorbid learning disorders, lower family income, and parental educational level. (Contains 3 tables.)