Aim Participation in education is one of the strongest social determinants of health, yet the majority of the literature has examined early childhood education. We examined whether there are additional benefits to completing upper secondary education compared to leaving education in early adolescence in a middle-income country.

Methods We performed a longitudinal analysis of the Cape Area Panel Study (CAPS), a survey of adolescents living in Cape Town, South Africa from 2002 to 2009. We undertook causal modelling using structural marginal models to examine the association between level of education completed and a variety of future health outcomes and behaviours, using inverse probability weighting (IPW) to control for confounders (sex, age, ethnicity, home language, income, whether employed in past year, region of birth, maternal educational status, marital status, whether currently pregnant and cognitive ability). Educational attainment was defined as primary education (grades 1–7), lower secondary education (grades 8–9) and upper secondary education (grades 10–12).

Results Of 3,432 participants in wave 4 (2006), 165 (4.8%) had only completed primary education, 646 (18.8%) had completed lower secondary and 2,621 (76.4%) had completed upper secondary school. We thus made lower secondary the reference group in these analyses.

Young people who had completed upper secondary education were less likely to have a chronic health problem or disability (OR 0.54, 95% CI 0.40–0.82; p = 0.004); have poor health (OR 0.58; 0.38–0.88; p = 0.01); report that health interferes with study or work (OR 0.65; 0.43–0.96; p = 0.03); smoked cigarettes in the past 30 days (OR 0.54; 0.44–0.68; p < 0.0001); been pregnant < 18 years (OR 0.34; 0.24–0.48; p= <0.0001); or had first sexual intercourse < 16 years (OR 0.52; 0.40–0.67; p < 0.0001) compared with those only completing lower secondary. No associations were found between education and alcohol or illicit drug use, psychological distress or obesity. Similar findings were obtained when upper secondary was compared with primary education.

Conclusion Completing upper secondary education was associated with a range of improved health outcomes compared with lower secondary or primary education. Secondary education offers low and middle-income countries an effective way of improving adolescent health.