Objective: This study evaluates the effectiveness of bystander sexual assault prevention education when the training of peer educators and delivery of prevention workshops were embedded in the undergraduate curriculum. Method: Participants were 827 undergraduate students (intervention, n = 518; control, n = 309). In a quasi-experimental design, students completed online surveys at 3 time points (baseline, 1-week postintervention and 4-month follow-up). Outcome measures included efficacy, readiness to change, intentions, perceived barriers to intervention, and behavior related to bystander interventions to sexual assault. Results: The intervention was effective in increasing students’ bystander efficacy, improving readiness to intervene by decreasing beliefs consistent with precontemplation and increasing those related to action, increasing intention to intervene, decreasing perceived skills deficits and concern about what others would think, and increasing proactive bystander behavior. The effects of the intervention were present for men and women and were observed in friendship and stranger contexts. All effects were maintained to 4-months without a booster. Conclusions: Integrating the preparation of peer educators and bystander-type sexual assault prevention workshops into the undergraduate curriculum can produce positive changes in male and female students’ confidence, readiness, and capacity to act as prosocial bystanders for friends and strangers, and increase some bystander behaviors.