Despite the high prevalence of comorbidity between attention deficit/hyperactivity disorder (ADHD) and learning disabilities (LD) or emotional disturbances (ED), few studies have examined the long-term effects of these comorbid relationships on student outcomes. We estimated the longitudinal academic, social, and behavioral outcomes in children with LD or ED comorbid with or without ADHD in a nationally representative sample of students receiving special education. We found that children with LD and ADHD had lower letter word identification scores, teacher-rated reading levels, and parent-reported social skills than children with LD alone. The differences between the two groups remained similar over time. Children with ED and ADHD had lower social skills and more classroom behavior problems and suspensions in schools than children with ED alone. Children with ED and ADHD also had slower growth in math calculation skills than children with ED alone over time. Implications for the education of children with comorbidity are discussed.