Educational leaders have sought to change the prevailing teacher-centered pedagogy to a student-centered approach. Despite the widespread awareness of the reform agenda, there is an increasing concern of whether a real instructional change happens in a way to promote students' mathematical development. This paper deals with successes and difficulties a teacher goes through as she moves on to student-centered instruction. The analysis draws on classroom observation and interviews to illustrate how the teacher and students establish social and sociomathematical norms that emphasize mathematical sense-making and justification of ideas. As such, this paper paves a way by which teachers and reformers open toward possibly subtle but crucial issues with regard to implementing reform agenda. [For complete proceedings, see ED496851.]