This paper reports a study into the development of staff understanding of assessment and assessment practice. Eight teachers from two universities constructed an initial concept map about assessment that was discussed in a one-to-one semi-structured interview. A year later, a new map was created and the interview focused on change in thinking and practice. Multiple models of assessment were evident in the participants' understandings at the same time and change was characterised by subtle evolution in thinking. Development in practice was more significant and often associated with the foregrounding of assessment for learning. Vignettes are used to illustrate the variation in nature and scale of development. Interplay between this development of practice and understanding was multidirectional and external context played an important role. The approach offers detailed insight into the relationship between assessment thinking and practice and demonstrates that both research and academic development need to go beyond conventional approaches to conceptualising the development of academics and take account of the finer grained complexities of assessment thinking and practices.