From the 1910s until the 1950s, the French administration in Mauritania funded several official médersas that provided a “Franco-Muslim” education to a select group of students in the towns of Boutilimit, Atar, Mederdra, Kiffa, and Timbedra. As its transliterated name suggests, the French médersa was a hybrid institution that combined elements of an Islamic madrasa and a French école. These schools were an important element in French politique musulmane, or “Muslim policy,” in that they trained young men to work as intermediaries with the colonial administration. Their explicit goal, in the words of their French creators, was the “domestication” (apprivoisement) of Mauritanian Muslims and the “containment” (canalisation) of Mauritanian Islam into channels that the French could control. The médersas of Mauritania were closely linked in several ways with médersas in Algeria. From 1850 until 1950, the French administration in Algeria ran three médersas in Algiers, Tlemcen, and Constantine. Those three schools trained students to work in legal and religious fields – as qadis in Islamic courts, as imams in mosques, and as teachers in Qur’anic schools. The Algerian médersas also sought to foster a “double culture” of both French and Islamic learning, exemplified by graduates’ mastery of both French and Arabic. It is not surprising, then, that when the administrators of Mauritania imported the médersa institution to that Saharan territory, Algerian médersa graduates were sent there to teach. In making the move from the Mediterranean to the Sahara, though, the ideal of the “double culture” was complicated by the distinctions, both real and imagined, between the categories of Algerian Islam and islam maure (“Moorish Islam”). This paper, based on interviews and archives in Algeria, Mauritania, and France, analyzes the experiences of those Algerian teachers and their Mauritanian students. It asks how the institution of the médersa, designed for certain purposes in Algeria, changed in response to differing demands on the part of both nomadic communities and French administrators in Mauritania. How did Algerians, trained in a certain “Franco-Muslim” curriculum, view their role in educating students in a significantly different colonial context? How did the category of “Muslim” change in its relationship to the different colonial administrations? In this paper I argue that the médersa, with its explicit educative mission, demonstrates the role of colonized individuals in shaping those categories in northwest Africa.