This paper is about social class and the teaching profession. While class has long been a core focus in the Sociology of Education, little attention has been paid to how it is conceived and enacted in the context of the professions, including teaching. While research in the area is increasing, we know relatively little about "the daily class work" of teachers, and student teachers, in schools. In the context of drives internationally to diversify the teaching profession, attention is needed to the experiences of those from lower socio-economic groups in their (generally) upwardly mobile trajectories. This paper draws on a constructivist grounded theory study about the social class identities and experiences of 21 student teachers from working class backgrounds as part of a wider teacher diversity project in Ireland. I present the concept of class chameleoning that was constructed from the data, being "different people" in different contexts, a behaviour that was reported by the participants as being very common, and in which the vast majority recounted participating, in their placement schools. This behaviour was motivated by a strong desire to fit in and to not be looked down upon, but resulted in significant bifurcation of the self. The analysis is interrogated using Goffman's dramaturgical analysis of social life and Bourdieu's habitus clivé (divided habitus), as well as key findings from research in teacher education. I end by pointing to the ethical implications of diversifying the teaching profession for under-represented groups without concomitant adaptation of the culture of the profession and schools.