Teaching for social justice in the mathematics classroom requires discernment between what "should" be done to ensure accountability to the practices of the discipline and what "could" be done to promote awareness of how those practices may be used to afford equity and access within the classroom. One approach to teaching and learning that may be used to promote discernment between the "should" and the "could" of the mathematics classroom is based upon the notion of "community of practice". This article explores written descriptions provided by students as they participate in a Year 7 mathematics classroom community of practice. Student descriptions are analysed in terms of student participation in the literacy practices of their mathematics classroom and in terms of the sense of agency that participation in these practices afforded different students. Connections are drawn between the development of student agency in the mathematics classroom and teaching for social justice.