BACKGROUND AND OBJECTIVES: Attention-deficit/hyperactivity disorder (ADHD) cohort studies have typically involved clinical samples and have usually recruited children across wide age ranges, limiting generalizability across complexity and developmental stage. We compared academic, emotional-behavioral and social functioning at age 10, and predictors of outcomes, in a nonreferred cohort of children recruited at age 7, between those with full-syndrome (FS) ADHD and controls with no ADHD. METHODS: This was a prospective cohort study with a 3-year follow-up period. Children were recruited from 43 socioeconomically diverse schools in Melbourne, Australia. Multi-informant outcomes at age 10 were academic functioning (Wide Range Achievement Test 4; Social Skills Improvement System), emotional-behavioral functioning (Strengths and Difficulties Questionnaire total), and social functioning (Strengths and Difficulties Questionnaire peer problems). Outcomes were compared across the groups by using adjusted random-effects linear regression analyses. RESULTS: In total, 477 children (62% male) were recruited at a mean (SD) age of 7.3 years (0.4). There were 179 participants with FS ADHD, 86 with ST ADHD, and 212 controls. Sample retention was 78.2% at 3-year follow-up. Both the FS and ST groups were functioning worse than controls on almost all outcome measures. The best predictors of outcome for children with ADHD were working memory (academic outcome, P < .001), ADHD symptom severity (emotional-behavioral outcome, parent: P < .001; teacher: P < .01), and autism spectrum disorder symptoms (emotional-behavioral outcome, parent P = .003; social outcome, parent P = .001). CONCLUSIONS: Children with FS and ST ADHD at age 7 experience persisting functional impairments across domains at age 10. The predictors identified at age 7 present potential targets for intervention to ameliorate impairments.