Objective: This study assessed the effectiveness of mutual aid groups for high school students. Methods: A quasi-experimental design was applied to 242 adolescents, where every other adolescent was assigned to the intervention or the control condition. The study evaluated the influence of implementing mutual aid groups in decreasing perceived risk of substance use, favorable attitudes toward substance use, and reducing substance use while increasing group engagement. Participants were assessed at baseline, during Sessions 2 and 7, and treatment exit. General linear mixed-effects models were used to detect significant differences between treatment and control conditions. Results: Findings indicated mutual aid groups significantly reduced favorable attitudes toward drug use and decreased alcohol and marijuana usage compared to the control group. In addition, the adolescents in treatment significantly increased their group engagement. Conclusions: Results support mutual aid group work models for reducing alcohol use and increasing group engagement for high school youth.