This article concentrates on Catholic mission teachers in Southern Tanzania from the 1890s to the 1940s, their role and agency in founding and developing the early education system of Tanzania. African mission teachers are an underrated group of actors in colonial settings. Being placed between colonized and colonizers, between conversion and civilising mission, between colonial rule and African demands for emancipation, between church and government and at the heart of local society, their agency was crucial to forming African Christianity, to social change and to a newly emerging class of educated Africans. This liminal position also rendered them almost invisible for historiography, since the colonial archive rarely gave credit to their vital role and European missionary propaganda tended to present them as examples of successful mission work, rather than as self-reliant missionary activists. The article circumscribes the framework of colonial education policies and missionary strategies, it recovers the teachers’ active role in the colonial education system as well as in missionary evangelization. Finally, it contrasts teachers’ self-representation with the official image conveyed in missionary media.