Background: Teen Prevention Education Program (PEP) is a school-wide, peer-led comprehensive sexuality education program currently implemented in more than 50 schools across 2 states. Many teen pregnancy prevention researchers and practitioners view peer-led programs as a promising approach for reducing teen pregnancy and associated sexual risk behaviors. However, prior research on the effectiveness of these programs indicates mixed results. Methods: We randomly assigned schools to implement Teen PEP immediately (intervention group) or on a delayed schedule (comparison group) and used propensity score matching to improve the comparability of the study groups. We surveyed students at baseline and about 6 months after the program ended. Results: Teen PEP did not significantly impact rates of sexual activity or unprotected sex; however, the program led to improvements in exposure to information about sexual health topics and knowledge of preventing pregnancy and transmission of sexually transmitted infections. Conclusions: Teen PEP succeeded in accomplishing some of its most proximal goals, increasing students' access to information and knowledge. However, we found little evidence that the program affects sexual risk-taking within 6 months of its conclusion. Future research will examine the program's longer-term impacts on sexual risk behaviors.