Massachusetts is the only state in the country that mandates annual Screening, Brief Intervention and Referral to Treatment (SBIRT) assessments in middle schools and high schools. SBIRT is a widely used model for screening emergent substance use. This five-year, cluster-randomized trial includes 40 public schools in Massachusetts and evaluates enhancements to SBIRT delivery. The study evaluates how near-peer support affects screening efficacy and student outcomes related to substance use risk. Exploratory qualitative analyses will evaluate implementation barriers and potential disparities in effectiveness for structurally marginalized student populations (NCT 06206161; AU-2022C1-26355).