My program of research concerns the meaningful engagement of students in mathematical practices and their development of increasingly more sophisticated ways of engaging in those practices. My research focuses, in particular, on practices related to algebraic reasoning and to mathematical argumentation (justifying and proving). A primary goal of my work is to develop sufficiently detailed accounts of learning and instruction in classroom contexts to guide the development of instructional practices, curricular materials, and teacher education/professional development aimed at facilitating students' mathematical development.