This study explored the relationship between sexual health indicators and the receipt of, and perceived relevance of, school-based sexuality education. Multiple regression analyses were conducted using data from 4,189 14- to 18-year-olds who participated in a cross-sectional Australian study. Receiving sexuality education was significantly associated with decreased STI risk, decreased experiences of unwanted sex, and better STI knowledge. High perceived relevance of the most recent sexuality education received was significantly associated with confidence and assertiveness in communication, intention to use condoms in the future, and STI knowledge. Sexuality education spanning multiple grades, incorporating topics about contraception, STI prevention and testing, different sexual practices, sexual and gender diversity, and information about sex in general, as well as involvement by an external educator, were significantly associated with higher perceived relevance of sexuality education. Perceived relevance of most recent classes decreased with age, highlighting the need for sexuality education early in the school years to ensure relevance and effectiveness. Findings suggest that strengthened teacher education, which will reduce the need for external educators and increase the frequency of classes, as well as consulting with students about their needs to improve the relevance of sexuality education, may improve young people's sexual health and experiences.