This article provides a geographical and urban analysis of the contribution of differences in enrollment between the public and private sectors to social segregation in French middle schools. Using the mutual information index, we show that the contribution of public/private divergences is higher in middle-sized urban areas and center municipalities. These geographical areas, however, are not those where social segregation is the highest, nor those where the private sector is commonly regarded as the main cause of segregation. Moreover, the gaps between the public and the private sectors are stronger at the local level. This confirms the idea that the private sector is indeed a tool for circumventing France's School Map (la carte scolaire) for allocating places to pupils and that private schools create additional social differences the smaller spatial scale.