This paper investigates the potential consequences of falling fertility on the reproduction of social inequalities over time. We develop a framework to understand how the fertility decline should interfere on the intergenerational transmission of disadvantages and apply it in the context of Ouagadougou, the capital city of Burkina Faso. We use data from the Health and Demographic Surveillance System (HDSS) of Ouagadougou, which collected retrospective data over three generations (grandmothers, mothers and children). We then use structural equation modeling (SEM) to estimate the models, and finally we conduct a sensitivity analysis to assess the consistency of our results. The results confirm that family size decline has a significant leverage on the intergenerational transmission of educational disadvantages. First, family size of mothers is significantly patterned by their grandmother’s characteristics, particularly education and socioeconomic status (SES). Second, mothers with reduced family size appear to invest more in the education of their children, which should enable them to maintain their educational advantages across generations with respect to poorer and non-educated families. These results remain robust after testing alternative assumptions about SES of grandmothers. Moreover, the findings also confirm that the relationship between educational investment and family size is changing over the course of socioeconomic development. While for recent generations (mothers and children) this relationship is strongly negative, for older generations (grandmothers and mothers) it is weak, albeit positive and statistically significant. This suggests that the meaning of the quantity of children and their participation in the labor force is shifting across generations in Ouagadougou, as in most urban areas in Africa.