College students are at particularly high risk for mental health problems, such as eating disorders, which are associated with functional impairment, distress, and morbidity, but barriers limit implementation of evidence-based interventions at colleges. We evaluated the effectiveness and implementation quality of a peer educator (PE) delivered eating disorder prevention program (the Body Project [BP]), which has a broad evidence-based using a train-the-trainer (TTT) approach and experimentally evaluated three levels of implementation support. We recruited 63 colleges with peer educator programs and randomly assigned them to (a) receive a 2-day TTT training in which peer educators were trained to implement the Body Project and supervisors were taught how to train future peer educators (TTT), (b) TTT training plus a technical assistance (TA) workshop (TTT + TA), or (c) TTT plus the TA workshop and quality assurance (QA) consultations over 1-year (TTT + TA + QA). Colleges recruited undergraduates (N = 1,387, 98% female, 55% White) to complete Body Project groups. There were no significant differences across condition for attendance, adherence, competence, and reach, though nonsignificant trends suggested some benefit of TTT + TA + QA relative to TTT for adherence and competence (ds = .40 and .30). Adding TA and QA to TTT was associated with significantly larger reductions in risk factors and eating disorder symptoms. Results suggest that the Body Project can be effectively implemented at colleges using peer educators and a TTT approach and that adding TA and QA resulted in significantly larger improvements in outcomes for group participants, and marginally higher adherence and competence. (PsycInfo Database Record (c) 2023 APA, all rights reserved).