Mathematics teaching as praxis recognises that teachers are required to continually make morally dense and value-laden decisions about their work. However, mathematics teachers' practice is constrained by the practice architectures of their ?eld. Therefore, to facilitate effective mathematics pedagogy, it is not enough to attend only to the teachers' practices without also working to reform the practice architectures within which they work. In this paper, data from interviews and observations with effective mathematics teachers are used to identify and explore aspects of classroom practice where students' broader mathematical identities are engaged. A praxis lens is employed to examine these aspects and discuss the moral and ethical dimensions of the teacher's decisions and actions, highlighting the implications for the development of students' mathematical identities. Finally, the data are examined to identify practice architectures that enhance or constrain the teacher's capacity for praxis and the student's opportunities to develop robust mathematical identities.