Early sexual debut is of major concern because it is a correlate for health and economic shocks experienced in adulthood. In South Africa, this concern has provided impetus for research directed at the HIV and AIDS epidemic, teenage pregnancy and the effect of adolescent sexual behaviour on persistence in school. Of interest to the present study is high school completion, which is a well-established empirical barometer of adult socioeconomic opportunities. Using data from the five waves of the Cape Area Panel Study (CAPS), this paper examines the association between sexual behaviours initiated in pre- and early adolescence and high school completion rates. The CAPS study is a longitudinal survey that was designed to investigate young people's (aged 14-22 years) educational attainment and sexual behaviours in Cape Town, South Africa. The sample was constituted from 3213 individuals who had initiated sex during their teenage years and the analysis was undertaken when the youngest cohort was aged 21, an age at which they should have completed high school if they were on time. Logistic regression models were fitted separately for males and females. Overall, the results reveal that early sexual debut is correlated with long-term negative educational outcomes. Individuals who experience early sexual debut are less likely to complete high school than their counterparts who make their sexual debut later on in life. This effect is worse for Africans, who also disproportionately have an earlier sexual debut than other race groups. Apart from race however, the findings also reinforce the effect of other demographic factors on high school completion, namely, place of residence and family socioeconomic status as measured by parental education and household income. Hence, early sexual debut adds another layer of inequality and worsens the plight of Africans, females, those living in rural areas and those who come from low-income families.