Research has shown that teachers can derive substantial benefits from the role of cooperating teacher (CT) and many experienced teachers have made positive changes to their teaching as a result, often engaging as co-learners. The aim of this paper is to examine the intricacies of the trajectory of CTs in terms of the development of their understanding of what an effective supervisor entails. Lave and Wenger's concept of legitimate peripheral participation is utilised to understand how teachers' learning trajectories enhance or inhibit the move towards full participation in effective school placements. The findings indicated that within the school placement the role of the CT is very influential but poorly prepared for and supported by the Higher Education Institution (HEI). Results have indicated mechanisms to potentially enhance existing policy and practice, develop the role of the CT and create a systemic shift in school-university partnerships.