In this systematic and critical review of purely school based child sexual abuse prevention program efficacy studies, 22 studies meeting the inclusion criteria differed by target population, program implementation, and evaluation methodology. Measured outcomes for children included knowledge, skills, emotion, risk perception, touch discrimination, reported response to actual threat or abuse, disclosure, maintenance of gains, and negative effects. Many studies had methodological limitations (e.g., sampling problems, lack of adequate control groups, lack of reliable and valid measures). However, most investigators claimed that their results showed significant impact in primary prevention (increasing all children’s knowledge or awareness and/or abuse prevention skills). There was little evidence of change in disclosure. There was limited follow-up evidence of actual use and effectiveness of prevention skills, and the evidence for maintenance of gains was mixed. Several programs reported some negative effects. Very few studies reported implementation fidelity data, and no study reported cost-effectiveness. Implications for future research, policy, and practice are outlined.