This study interrogates how beginning secondary mathematics teachers align their beliefs with their practice when they justify their pedagogical choices in the context of recent English mathematics education policy which is strongly influenced by approaches to mathematics teaching in Shanghai and Singapore currently referred to as 'mastery' approaches. It seeks to understand beginning teachers' perceptions and understandings of these approaches and the extent to which they recognise aspects of 'mastery' in practice. In setting the context, pre-service teachers' beliefs were surveyed and found to be congruent with constructivist approaches to learning. We then draw on qualitative data from semi-structured interviews secondary mathematics teachers in their first year post-qualification. The interviews were designed to interrogate and capture understanding of the features of mastery within their own classrooms. By using vignettes to capture participants' beliefs, our aim was to present a 'more nuanced understanding of the phenomena' (Skilling and Stylianides in Int J Res Method Educ 43(5):541-556, 2019, 10.1080/1743727x.2019.1704243). The analytical framework developed draws on Guskey's (In: Wright J (ed) International encyclopedia of the social & behavioural sciences, 2015, vol 14, 2nd edn, Elsevier, pp 752-759) interpretation of Bloom's theory of mastery learning together with features of mastery learning in mathematics articulated by Drury (How to teach mathematics for mastery, 2018, Oxford University Press) and Boylan et al. (Edu Sci 8(4):202, 2018, 10.3390/educsci8040202). This posed a research design challenge given the variation in interpretation of mastery learning as it is understood in practice. The data exposes differences in the interpretation of mastery approaches in the settings where they learn to teach, as well as the tensions that arise between beginning teachers' beliefs, practice, professional knowledge and agency in their developing classroom roles.
