Results of a 3-year randomized clinical trial of Second Step: Student Success Through Prevention (SS-SSTP) Middle School Program on reducing bullying, physical aggression, and peer victimization among students with disabilities are presented. Teachers implemented 41 lessons of a sixth- to eighth-grade curriculum that focused on social-emotional learning (SEL) skills, including empathy, bully prevention, communication skills, and emotion regulation. Two school districts in a larger clinical trial provided disability information. All sixth-grade students (N = 123) with a disability were included in these analyses, including intervention (n = 47) and control (n = 76) conditions. Linear growth models indicated a significant intervention effect for bully perpetration; compared with students in the control condition, intervention students' bullying perpetration scale scores significantly decreased across the 3-year study (d = -0.20, 95% confidence interval = [-0.38, -0.03]). SEL offers promise in reducing bully perpetration among students with disabilities.