Background: Addressing school violence is an important public health goal. To assess the role of school mental health curricula in violence prevention, we evaluated effects of an anti-stigma curriculum on violence victimization/perpetration. Methods: An ethnically/socioeconomically diverse sample of 751 sixth-graders (mean age 11.5 years) across 14 schools in Texas were block-randomized by school (2011-2012) to receive singly or in combination: (1) a mental illness anti-stigma curriculum; (2) contact with 2 young adults with mental illness; or (3) merged control (printed materials/no intervention). Pre- and post-test assessments were self-completed during health education classes; prior to randomization, 484 (64.5%) agreed to 2-year, home-based longitudinal assessments. Statistical models tested short- and long-term effects on physical, verbal, and relational/social violence victimization/perpetration. Results: At 1-month post-test, students who received the "curriculum" versus control made fewer verbal threats (p < 0.05). Those with high-level mental health symptoms in the "curriculum" group versus control used less violence overall and received fewer verbal threats from peers short-term (p < 0.05). "Curriculum" effects of reducing violence perpetration sustained long-term among adolescents with high-symptoms (p < 0.01). The comparator "contact" intervention was ineffective short- and long-term. Conclusions: Implementing efficacious mental health curricula can serve as a multi-pronged strategy with anti-bulling efforts to prevent violence and improve mental health.