This study examines whether offering sex education to young teenagers affects several measures of adolescent sexual behavior and health: virginity status, contraceptive use, frequency of intercourse, likelihood of pregnancy, and probability of contracting a sexually transmitted disease. Using data from the National Longitudinal Study of Adolescent Health, I find that while sex education is associated with adverse health outcomes, there is little evidence of a causal link after controlling for unobserved heterogeneity via fixed effects and instrumental variables. These findings suggest that those on each side of the ideological debate over sex education are, in a sense, both correct and mistaken. Opponents are correct in observing that sex education is associated with adverse health outcomes, but are generally incorrect in interpreting this relationship causally. Proponents are generally correct in claiming that sex education does not encourage risky sexual activity, but are incorrect in asserting that investments in typical school-based sex education programs produce measurable health benefits.