Background: Owing to the associations between diet and health, it is important that effective health promotion strategies establish healthful eating behaviors from an early age. We reviewed the intensity of school-based interventions aimed to modify dietary behavior in preadolescent and adolescents and related intervention characteristics to effectiveness. Methods: Our systematic literature search of 8 databases sought to identify interventions measuring dietary intake in school settings to students aged 9 to 18. We evaluated these studies for effectiveness, intensity, intervention category, and follow-up measures. Results: Of the 105 interventions 81 were found to be effective immediately postintervention, irrespective of intensity. Studies that were 6 weeks to 5 months in duration, targeted students' environment or group (alone or in combination), and reached students only in schools were more effective. Only one-fifth of interventions conducted a follow-up measure, and a majority showed a loss of effectiveness from postintervention to follow-up. Conclusions: We identified characteristics of effective interventions. These findings may inform the development of future interventions targeting dietary behavior in preadolescents and adolescents in the school-based setting.