This article describes the findings from an efficacy trial of a school-based, universal prevention program designed to reduce aggressive behavior of by strengthening emotion regulation and social information-processing (SIP) skills. Three cohorts of third graders (N = 479) participated in this study. The first cohort participated in the Making Choices (MC) program, a second cohort participated in the Making Choices Plus (MC+) program, and a third (lagged) cohort received the standard health education curriculum. Pretest to posttest changes suggest both programs were associated with reduced levels of aggression and improved SIP skills. Gender-moderating effects were observed--boys displayed significant reductions in aggressive behavior and significant increases in positive social goals, whereas girls' aggressive behaviors and social goals showed no significant changes.