OBJECTIVES We conducted a cluster randomized controlled trial to test the a priori hypothesis that students attending an intervention middle school would be less likely to report physical adolescent relationship abuse (ARA) 1 year later compared with students attending a control school. Secondary objectives were to determine if the intervention reduced substance misuse, bullying, and fighting. METHODS Twenty-four Texas public middle schools were matched by the size of student enrollment, number of economically disadvantaged students, and race and ethnicity of the student body and randomly assigned to the intervention (n = 12; 1237 participants) or the control (n = 12; 1531participants) group. The intervention, Fourth R, is a classroom-based curriculum delivered by existing teachers and consists of 21 lessons on injury prevention, substance use, and growth and development. RESULTS Participants (50% female) self-reported ethnicity as Hispanic or Latinx (35%), Black or African American (24%), Asian American (17%), White (8%), and multiethnicity or other (16%). Among those who have dated, students in the intervention schools were less likely to report perpetrating physical ARA (intervention = 14.9% versus control = 18.3%) relative to students in the control schools (adjusted odds ratio, 0.66; 95% confidence interval, 0.43–1.00; P = .05). In the overall sample, no significant differences emerged between control and intervention groups with respect to substance misuse, fighting, and bullying. CONCLUSIONS The middle school version of Fourth R is effective in reducing physical ARA perpetration over at least 1 year. The intervention did not have an effect on bullying perpetration, physical fighting with peers, and substance misuse. Long-term assessment, especially follow-up that covers the transition to high school, is needed to examine the program benefit on key outcomes.