The main aim of this article is to identify systematic reviews of the effects of developmental prevention programs. These programs are defined as community-based programs designed to prevent antisocial behavior, targeted on children and adolescents, and aiming to change individual, family, or school risk factors. Only evaluations that reported effects on the outcomes of delinquency, offending, violence, aggression, or bullying were included. In total, 50 systematic reviews were assessed: five general reviews, 11 reviews of individually focused interventions, nine reviews of family-based programs, and 25 reviews of school-based programs. It was possible to calculate effect sizes from 33 reviews. Every summary odds ratio effect size was greater than 1, indicating that all types of programs were effective. The effect size was statistically significant in all except four cases. The median effect size was 1.46, which corresponds (on some reasonable assumptions) to a decrease in aggression of about one quarter. This article makes recommendations about how to improve systematic reviews and concludes that more investment in developmental prevention is warranted. (C) 2016 Elsevier Ltd. All rights reserved.