This paper considers the notion of 'criticality' in relation to the Masters in Teaching and Learning (MTL), the Teacher Development Agency (TDA)-funded masters programme for school teachers in England. After the two current cohorts complete the MTL in 2013 - one a cohort of Newly Qualified Teachers (NQTs) and one of more senior Teaching and Learning Responsibility holders (TLRs) - government funding will not be provided for any subsequent recruitment to the course. In light of this, debates around the MTL may be viewed as redundant, but we do need to acknowledge that there will be a cohort of students who hold a Masters in Teaching and Learning and for whom it is a valid qualification. Beyond this, discussion of what a masters course in education might consist of is still a relevant and urgent matter. Our argument in this paper draws upon our experience of working on the MTL but is, we submit, applicable more generally to the 'practice-based' masters courses that have proliferated in recent years. Our focus is upon criticality as an essential component of 'masterliness'. We consider briefly ways in which critique might be construed and practised before going on to argue that a certain idea of critique, which draws upon historical conceptions of education's role in serving the social good, is essential to educational practice and to claims to mastery in education. We conclude by drawing attention to difficulties that may be presented to teacherresearchers on master's courses that offer themselves as school-based programmes of professional development