Teacher leadership is a concept that is gaining increasing interest from both practitioners and researchers. This article presents findings from three case studies in the UK that can be characterized as exhibiting developed, emergent and restricted teacher leadership. Differences and similarities between the schools were examined, leading us to conclude that purposive action by the head, school culture and school structures were the key distinguishing factors. Teacher leadership requires active steps to be taken to constitute leadership teams and provide teachers with leadership roles. A culture of trust and collaboration is essential, as is a shared vision of where the school needs to go, clear line management structures and strong leadership development programmes. In the developed and emergent teacher leadership schools, barriers to teacher leadership were mainly external to the school. In the school we described as exhibiting restricted teacher leadership, internal factors were also key barriers. (Contains 2 tables.)