This paper takes its departure from an interactive study conducted in a Swedish secondary school during 2008-2011. The aim is to study the practice of teachers’ continuing professional development (CPD) in a teacher team involving peer group mentoring (PGM) to find out how and what kind of teachers’ pedagogical knowledge and expertise that is constructed. And to examine how the PGM-practice was constrained and enabled and what kind of CPD was made possible. The theoretical framework is based on practice theory. Practice architectures are used to uncover the relations between the PGM-practice and its historical, material-economic, social-political and cultural-discursive conditions. The methodological approach is action research. A main finding is that professional and personnel development may be imposed through PGM. Democratic process increased during the PGM-meetings and seemed to have an impact on classroom practice and the practice of parent-teacher meetings as well. Furthermore, the PGM-practice and its outcomes are deeply interconnected to global and local historical, material-economic, social-political and cultural-discursive arrangements which constrained and enabled it. When economic cut downs began to take effect in the local school, along with a neo-liberal discourse, democratic processes were challenged and threatened. The focus in the PGM-discussions shifted from the teachers’ perceived need for pedagogical knowledge development to talk about students as costs. A collegial approach and the ability to carry out reflexive cooperation were both fostered by the model and articulated in the PGM-practice as important teacher skills.