Sex education is a controversial topic in many countries. Research on the effectiveness of sex education is optimistic, but the content of sex education learned by teenagers is often unknown. Using data from the National Child Development Study of Great Britain, this study examines the sex education lessons reported at age 16 by subjects and their school headteachers, and the subjects’ report of teenage motherhood at age 23. Results show that sex education may be associated with teenage motherhood either positively or negatively, depending on the topic and the marital status of the individual when she became a teenage mother. Implications for continuing debates on the worth and effectiveness of sex education are discussed.