Over the last few decades, research has widely acknowledged and emphasised the interactional role of language in teaching and learning mathematics in primary classrooms. This chapter takes a discursive approach and uses Bakhtin’s concept of speech genres to explore how the teacher and children (aged 9–11) in a Year 5/6 classroom use different ways of talking to display their understanding of geometric shapes during classroom interactions in a New Zealand English-medium primary school. The analysis suggests that the teacher and children use a variety of speech genres embedded with prosodic features from their repertoire of languages to participate as well as interactionally construct mathematical meanings as they engage in classroom discussions. The use of multiple speech genres in any classroom provides us with insights not only into what children and the teacher construct as mathematical in the real sense, but also allows us to delve deeper into the aspects of participation in the classroom. The chapter finishes with a few implications for teaching and research.