This paper explores the social positions that students construct and the patterns of participation that different individuals and groups achieve within a classroom community of practice. Using a form of collective argumentation to promote student involvement in the practices of a disciplinary community of mathematicians, the study employed a participant-observation design to explore Year 7 students' "talk about" and "talk within" a classroom community. Through examining "talk about", as evidenced in journal writings, and "talk within", as displayed in a group presentation, one female student's journey towards more mature ways of participating in her classroom community is tracked and discussed. The student, Cath, is a high-achieving student who attends a primary school located near the centre of a capital city in Australia. Cath's Year 7 class is made up of 26 (11-12-year old) male and female students. The study found that as a student moves towards greater levels of participation in the classroom community, he/she may construct social positions that are marked by changing relationships between themselves and the discipline of mathematics. The study found also, that the cultural resources of a mathematical community, such as norms of participation, are important rudiments of long-term change in the social positions that students construct. Findings are presented in a manner that demonstrates how sociocultural theory may function to inform and describe student participation in classroom learning.