Summary Background In addition to the inherent importance of education and its essential role in economic growth, education and health are strongly related. We updated previous systematic assessments of educational attainment, and estimated the contribution of improvements in women's education to reductions in child mortality in the past 40 years. Methods We compiled 915 censuses and nationally representative surveys, and estimated mean number of years of education by age and sex. By use of a first-differences model, we investigated the association between child mortality and women's educational attainment, controlling for income per person and HIV seroprevalence. We then computed counterfactual estimates of child mortality for every country year between 1970 and 2009. Findings The global mean number of years of education increased from 4·7 years (95% uncertainty interval 4·4–5·1) to 8·3 years (8·0–8·6) for men (aged ≥25 years) and from 3·5 years (3·2–3·9) to 7·1 years (6·7 −7·5) for women (aged ≥25 years). For women of reproductive age (15–44 years) in developing countries, the years of schooling increased from 2·2 years (2·0–2·4) to 7·2 years (6·8–7·6). By 2009, in 87 countries, women (aged 25–34 years) had higher educational attainment than had men (aged 25–34 years). Of 8·2 million fewer deaths in children younger than 5 years between 1970 and 2009, we estimated that 4·2 million (51·2%) could be attributed to increased educational attainment in women of reproductive age. Interpretation The substantial increase in education, especially of women, and the reversal of the gender gap have important implications not only for health but also for the status and roles of women in society. The continued increase in educational attainment even in some of the poorest countries suggests that rapid progress in terms of Millennium Development Goal 4 might be possible. Funding Bill & Melinda Gates Foundation.