In this study, the oral conversations of primary students were examined in an effort to understand how student participation and role in discourse community affects their learning. Discourse analysis provided both an analytical framework for analysing student and teacher talk and a definition of discourse communities. The concept of discourse communities carries with it an argument for the dialogic or constantly reconstructed "self". The focus of this paper is the analysis of one discussion among three grade-2 (ages seven to eight years old) students and the researcher. The students bring with them varying expertise, and are constantly co-creating their "selves" in different small-group discourse communities. By using discourse analysis as an analytical framework, it becomes easier to determine the different roles that students and teachers play, the different selves that are co-created, and the possible impacts of these on student learning. The analysis reveals the complexity that primary-school teachers encounter as they attempt to set up discourse communities in which all students can actively participate as learners.