This article expands the scope of comparative social stratification research in education to rapidly developing, largely low-income sub-Saharan Africa. First, we investigate trends in the association between parental socioeconomic status (SES) and children's chances to attend and complete primary education, exploring whether and where educational expansion of the early twenty-first century led to equalization of educational opportunities. Drawing on data from 153 Demographic and Health Surveys and Multiple Indicator Cluster Surveys (1990-2017) from 40 countries, findings indicate that inequality in attendance declined, but inequality in completing six grades largely persisted. Cross-country analyses reveal a large variation in inequality levels and trends. We explore the role of national contextual factors and find that underweight prevalence, fertility rates, school fees, public spending on education, and the ratio of pupils to teaching staff systematically explain variation in SES gaps across countries and cohorts. Findings underline the importance of absolute material deprivation and school teaching resources in the stratification of educational opportunities in this region.