PurposeThis study examined the association of individual, family, and school-level characteristics with age of sexual initiation (ASI) and focused specifically on school context as a moderator of known predictors of ASI. MethodsData are from Waves I and IV of the National Longitudinal Study of Adolescent Health (N = 10,596). Predictors include grade point average, physical development, attitudes about sex, likelihood of higher education, alcohol use, delinquency, family structure, parents' education level, childhood abuse, maternal approval of sex, parental monitoring, and parent–child relationship quality. School-level predictors are averages of adolescents' attitudes about sex and likelihood of higher education and parents' education. Hierarchical linear models run separately by sex were used to predict ASI. ResultsWhen school-level attitudes about sex are more favorable, both boys and girls report younger ASI, and school mean parental education attainment moderates the influence of individual adolescents' attitudes about sex on ASI. More of the predictors are significant for girls than boys, whereas perception of maternal and peer approval of sexual activity are the most salient predictors of younger ASI for boys. ConclusionsResults highlight the importance of school context for understanding adolescents' motivations for early ASI. Findings support the need for school-wide prevention interventions that engage adolescents, peers, and parents in addressing attitudes about early sex.