Objective: The aim of this study was to synthesize published data regarding long-term effects of ADHD on information learned (measured via achievement tests) and success within the school environment (academic performance). Method: A systematic search identified 176 studies (1980-2012) of long-term (≥2 years) academic outcomes with ADHD. Results: Achievement test outcomes (79%) and academic performance outcomes (75%) were worse in individuals with untreated ADHD compared with non-ADHD controls, also when IQ difference was controlled (72% and 81%, respectively). Improvement in both outcome groups was associated with treatment, more often for achievement test scores (79%) than academic performance (42%), also when IQ was controlled (100% and 57%, respectively). More achievement test and academic performance outcomes improved with multimodal (100% and 67%, respectively) than pharmacological (75% and 33%) or non-pharmacological (75% and 50%) treatment alone. Conclusion: ADHD adversely affects long-term academic outcomes. A greater proportion of achievement test outcomes improved with treatment compared with academic performance. Both improved most consistently with multimodal treatment.