Previous studies have paid considerable attention to the impact on a child’s primary education of attending pre-primary school. Researchers have asserted that early educational intervention can compensate for the effects of poverty and inadequate learning environments on child development and school success. This study analyzes the relationship between pre-primary education and student reading and mathematics achievement in the sixth grade, focusing on disadvantaged children, in countries that participated in the Southern and Eastern Africa Consortium for Monitoring Educational Quality (SACMEQ) III project. The results show that the achievement of children who attended pre-primary education is higher than that of those who did not. The achievement of children who have many home resources for learning is better than that of children who have a few such resources. In almost all countries, disadvantaged children’s achievement is increased when they attend pre-primary education. However, the contribution of preprimary education to ameliorating social inequalities is different in the various contexts of different countries. These findings contribute to the discussion on the importance of early childhood care and education, especially in sub-Saharan Africa.