Abstract
Partnerships in education developed in schools in the 1990s to bring answers to new socio-educational problems. Nevertheless, for the teachers of the sandwich training, they establish for a long time the indispensable condition of a really professional co-op education program. By using the sociology of the actor-network and to the concept of social relationships, we would like to qualify this speech. From the analysis of two university co-op programs, we highlight that an almost fusional partnership with an occupational environment does not guarantee necessarily a harmonious professional development, and that the absence of partnership is not still the synonym for an absence of professionalization.