There is an increasing awareness of the social dimension in mathematics teacher education. Collaboration and co-operation are regarded as key factors in professional development. In this paper I will analyse some tensions that might arise when the professional development of mathematics teachers is considered a collective enterprise. I will present "phenomenological group" interview as a method that is designed to reveal the collective character of teacher development. Some primary teachers' collective reflections on an ongoing professional development process will be interpreted by focusing on the concepts of "routine" and "collective orientation". The discussion is centred on the ambivalence of routines, as facilitators of practice, and collective orientations, as socially-agreed-upon knowledge base, for mathematics teachers' professional development.