The negative consequences for victims and perpetrators of school violence are significant, multifaceted and, if left unchecked, can have personal costs that may last well into their adult lives. Universal violence preventive interventions may not be sufficiently effective in mitigating problems among middle school youth who exhibit risk of violent behavior. School-based mental health (SBMH) approaches show promise for reducing problems among the minority of youth responsible for violence perpetration, although the impact of teacher-delivered SBMH has been somewhat limited. The present study examines the impact of "practitioner"-delivered SBMH in middle school settings, with (a) a three-armed randomized controlled trial (RCT) comparing Expanded SBMH and Enhanced SBMH to Standard SBMH and (b) a separate quasi-experiment comparing the three SBMH arms in the RCT to a separate set of non-randomized, non-SBMH schools. SBMH schools who expanded their services saw decreases in aggressive behavior and victimization, across both study structures, that were either statistically significant, meaningful based on Cohen effect size conventions or both. These results suggest that the expansion of practitioner-delivered mental health services to youth who are at risk of violence perpetration, "but would otherwise be ineligible for, or unable to afford, services" achieves a significant impact on the larger school environment.