Background: While the potential benefits for educational investment of decline in family size are well known, some questions have emerged on the distribution of these benefits. Do all the children in a family benefit equitably from the improved conditions brought about by limiting their number? And what are the consequences of reduction in family size for social inequalities in educational opportunity within the family? Objective: This study aims to analyze the inequalities in education between children within the same family in the context of falling fertility in Ouagadougou, the capital city of Burkina Faso. Methods: Inequalities in school attainment are analyzed, first in regard to family sizes and second in terms of gender, birth order, and the interactions between these two variables. Probit models are estimated and adjusted Wald F statistics with Bonferroni corrections for multiple comparisons are computed. Results: The results show that family households with fewer children exhibit different patterns of investment in children's schooling, with lower inequalities between children by gender and birth order. At the post-primary level, however, the firstborn girls in small families appear to be less likely to be enrolled in school compared with those in large families, and also to be disadvantaged in their schooling compared to other children of small families. Conclusions: Reduced fertility appears to have negative effects on the schooling of the oldest girls and beneficial effects for all other children in the household. To mitigate this disadvantage, measures should be considered to reconcile domestic work with the new opportunities emerging from expanding school systems and smaller family sizes.