At the heart of changing institutional assessment and feedback practices is the need to transform university teachers' ways of thinking about feedback and assessment. In this article, we present a case study of a three-year Master's in Education offered to UK STEMM university teachers as an opportunity to develop critically reflective and theoretically underpinned approaches to their practice. We outline the extent to which, in Mezirow's terms, through a disorientating combination of studentship, self-reflection and paradigm crossing, the programme has the potential to change the participants' frames of reference. Drawing on our experiences of working with these students and in-depth interviews we discuss the impact the programme has had on the participants' assumptions around feedback and assessment, their identity, own practice and wider institutional perspectives and practice. Barriers identified by participants that inhibit assessment and feedback change are also explored.