The goal of this article is to investigate the symptom dimensions of oppositional defiant disorder (ODD; irritability, defiance) and attention deficit/hyperactivity disorder (ADHD; inattention, hyperactivity-impulsivity) as predictors of academic performance, depressive symptoms, and peer functioning in middle childhood. Children (N = 346; 51% female) were assessed via teacher-report on measures of ODD/ADHD symptoms at baseline (Grades K-2) and academic performance, depressive symptoms, peer rejection, and victimization on 7 occasions over 4 school years (K-2 through 3-5). Self-report and grade point average data collected in Grades 3-5 served as converging outcome measures. Latent growth curve and multiple regression models were estimated using a hierarchical/sensitivity approach to assess robustness and specificity of effects. Irritability predicted higher baseline depressive symptoms, peer rejection, and victimization, whereas defiance predicted higher baseline peer rejection; however, none of these ODD-related effects persisted 3 years later to Grades 3-5. In contrast, inattention predicted persistently poorer academic performance, persistently higher depressive symptoms, and higher baseline victimization; hyperactivity-impulsivity predicted subsequent peer rejection and victimization in Grades 3-5. In converging models, only inattention emerged as a robust predictor of 3-year outcomes (viz., grade point average, depressive symptoms, peer rejection, and relational victimization). Broadly, ODD dimensions-particularly irritability-may be linked to acute disturbances in social-emotional functioning in school-age children, whereas ADHD dimensions may predict more persistent patterns of peer, affective, and academic problems. By examining all 4 ODD/ADHD symptom dimensions simultaneously, the present analyses offer clarity and specificity regarding which dimensions affect what outcomes, and when. Findings underscore the importance of multidimensional approaches to research, assessment, and intervention.