Professionalism is a focus for student learning in many disciplines. It is known, furthermore, that interpersonal interactions between staff and students constitute an informal curriculum that has a significant influence on students. But the origins of this informal curriculum are not fully apparent. This article offers a multiple case study that explores the genesis of tutors' facilitation practices in small group medical teaching. Facilitation practices were seen to develop in response to a wide-ranging set of social, professional and critical concerns, affecting notions of professionalism promoted to students. Most tutors exhibited a mode of reflexivity that was extended in time and reach, with tutors also progressing mutual actions through communal deliberation. We thus identify ways in which the informal curriculum is grounded in both the primary agency and the corporate agency of tutors. In looking to promote professionalism, it is essential that curricula are staff- as well as student-centred.