In multilingual settings, selecting a medium of instruction (MoI) has been widely debated. While proponents advocate for using the official MoI, others support using the mother tongue or adopting bilingual/multilingual MoI. Despite the potential for each MoI model to contribute to learning inequalities among students, there needs to be more evidence regarding the specific categories of students and contextual factors involved. This study focuses on fourteen French-speaking Sub-Saharan African countries (Benin, Burkina Faso, Burundi, Cameroon, Chad, Congo, Côte d'Ivoire, Democratic Republic of Congo, Gabon, Guinea, Madagascar, Niger, Senegal, and Togo) to investigate disparities in learning outcomes between students exposed to the official MoI and those exposed to a bilingual/multilingual MoI. Leveraging data from PASEC 2019, the study employs Residualized Quantile Regression (RQR) as its analytical method. The findings indicate that each MoI model may result in learning outcome disparities, with the extent of inequality varying according to students' performance levels (low, average, or high achievers). Additionally, these disparities are influenced by factors such as the student's urban or rural residence and the specific characteristics of the educational system in place. These findings underscore the importance of developing language-in-education policies that consider students' characteristics (e.g., ability) and contextual factors.