This paper reflects on the implementation of a peer-assessment innovation in a large first-year geography unit. While the innovation had been carefully researched, difficulties in the implementation drew the authors' attention to the need for more change management to be built into the design and development. Focusing specifically on the teacher perspective, they describe the need for adequate development for all teaching staff to avoid miscommunication and variable implementation. Only on reflection did they realize that was a distinction between cooperation and commitment of members of the teaching team involved in this peer-assessment exercise. This resulted in patchy implementation and different levels of satisfaction being reported by different classes. They suggest that innovation implementation requires active learning strategies for staff who have not been involved in the design process. Given that extensive staff development activities are not possible because teachers are already overloaded, a critical friend approach might help encourage the whole teaching team to commit and more successfully implement change. (Contains 3 tables and 2 figures.)