School-based social-emotional (SEL) programs that address interpersonal conflict and teach emotion management have succeeded in reducing youth aggression among elementary school youth, with few studies in middle schools. Results of a two-year cluster-randomized (36 schools) clinical trial of Second Step Middle School Program (Committee for Children, 2008) on reducing aggression and victimization are presented. Teachers implemented 28 lessons (6th & 7th-grade) that focused on social emotional learning skills (e.g., empathy, problem-solving). All 6th graders (n=3658) completed self-report measures assessing bullying, aggression, homophobic name-calling and sexual harassment at three waves. Multilevel analyses revealed significant intervention effects for two of the seven outcomes. Students in intervention schools were 56% less likely to self-report homophobic name-calling victimization and 39% less likely to report sexual violence perpetration than students in control schools in one state. SS-SSTP holds promise as an efficacious program to reduce homophobic name-calling and sexual violence in adolescent youth.