Various kinds of mentoring processes to enhance teachers' collective learning and professional development have become popular. Collective learning and collective practice development within professions may be approached as an integral part of 'professional learning communities'. Research emphasises that learning communities cannot be commanded into existence and that they require voluntary participation. It is implicit that the participating teachers are open-minded and willing to share their teaching experiences. Yet in this article the situation is different. The article draws on a three-year-long case study in a Swedish secondary school involving one teacher team 'forced' to participate in peer group mentoring. The project aimed to develop teaching team facilitation using a nine-step model of peer group mentoring (PGM). Framed by Michel Foucault's notion of power, the analysis shows that the disciplining practice of PGM generated new and complex processes. These processes can be described as disciplining, democratising and developmental for both the individual and the teacher team.