This paper outlines an approach to improving learning and teaching that combines two strong research bases: The research on formative assessment or assessment for learning provides information about what to change; research on teacher learning communities guides decisions about how to change. In this paper we describe the content and process for one model of teacher professional development. Two case studies for two school districts engaged in this process of teacher change are then presented along with descriptions of the observed effects on both the participating teachers and their larger school contexts.