This article uses Wenger’s (1998) theory of communities of practice as a framework to describe the complexities of moderation processes when these processes are intended to support teacher learning in ways that subsequently help lift student achievement. We draw on a case study in which we observed teachers working together to moderate students’ writing in a school that had an established reputation for good assessment practice. We discuss these observations in relation to Wenger’s four attributes of a community of practice: practice, community, meaning and identity. Our purpose is not to prescribe “ideal” practice but rather to highlight the effort and commitment required to develop and maintain a community of practice around moderation processes that strengthen the professional knowledge teachers bring to their classroom practice. Developing and sustaining a robust community of practice for moderation purposes entails important leadership work and a strategic alignment between moderation practices and other systems and processes in the school.