This paper makes the claim that student teachers' learning depends a great deal on the individual school department where they are working, its social practices and the relationships of the teachers involved in initial teacher education (ITE). The paper considers how using a Cultural Historical Activity Theory (CHAT) lens to view data generated on school ITE activity helps to focus vital social, cultural and historical dimensions of practice. The research uses an activity system as a descriptive heuristic to explore whether understandings of the object and tools of school-based ITE activity systems are shared. The findings illustrate differences in the kinds of teacher learning possible, afforded in relation to the ways in which the object of the ITE activity system was constructed, and the tensions that emerged in interaction with other related activity systems. The necessity of negotiating and renegotiating the system's object regularly is emphasised in order for collaborative work in ITE to be successful in helping create opportunities that develop teachers through expansive learning. (Contains 1 table and 2 figures.)