My research examines the role of mathematical thinking in whole class discourse. Initially a study exploring the nature of discourse in some Irish primary mathematics classes was carried out. Six recordings of mathematics lessons from four different teachers were analysed using the Math Talk Learning Community framework (Huffed-Ackles, Fuson & Sherin, 2004) and Boaler and Brodie’s (2004) teacher question categories. Student thinking shared in whole class discourse in these lessons seemed to be limited by the teachers’ central role as evaluative authority and source of mathematical ideas. The aim of the second stage of my research was to create a discourse community in my own classroom. This involved positioning students as mathematical authorities capable of evaluating mathematical thinking. It was envisaged that the resulting classroom discourse would be progressive and mirror discourse at domain level (Bereiter, 1994). Thirty-one recordings on fractions, decimals and percentage topics were collected, fourteen of which were transcribed. Five of these lessons were analysed in the same manner as at stage 1. This analysis showed that student thinking became an object of discussion in the teaching experiment lessons as students commented on and evaluated the thinking of their peers. The participation trajectories (Dreier, 1999; 2009) of ten students were tracked across the fourteen transcribed lessons with a view to documenting students’ use o f discourse community practices such as explaining and justifying thinking, or disagreeing with previous contributors. Despite initial concerns over the participation o f lower achievers, this analysis showed that all students participated in the practices of the discourse community to some extent. However it also highlighted differences in the nature of the experience for different individuals. 1 also interrogated my own experience as teacher-researcher to investigate the issues involved in facilitating a discourse community. This analysis suggested that many of the dilemmas experienced by the teacher are managed rather than resolved (Lampert, 1985)