This longitudinal case study examines whether a school-based training scheme that brings together different categories of teacher educators (university supervisors and cooperating teachers) engenders true collective training activity and, if so, whether this collective work contributes to pre-service teacher education. The scheme grew out of a recent French reform policy. The study is based on an original theoretical conception of teacher education that borrows postulates from a theory of learning and collective action (Wittgenstein 1996). Illustrated by excerpts from post-lesson meetings and self-confrontation interviews, the results suggest that the training scheme does not always lead to collective training activity. The difficulties are notably due to disagreement between the educators about attributing meaning to the pre-service teacher's classroom activity, which hampers professional development. On this basis, proposals are made to contribute to an effective and authentically shared supervision process and to reposition training activity at the heart of the processes of pre-service teacher professional development.