French immersion is a program that some non-native French parents in Canada choose for their children. Some time allocation models for French immersion programs mean that students in French immersion classes will study mathematics in French and in English at different times during their educational careers. This study follows an elementary class of French immersion students from grade three, when the language of mathematics instruction is French, to grade four, when the language of mathematics instruction changes to English. Using Sfard’s four categories of discourse: routine, endorsement, visual mediators, and word use, transcripts of audio recordings of teacher and student language in the classroom were analysed. The characteristics of the teacher and student discourse, as well as the similarities and differences between mathematical discourse in the French language and English language mathematics classrooms were described. The data was characterised by two routines: a question-response-endorsement routine, and an exploratory routine. Although both routines were found in both the French language and the English language classrooms, there were differences as well as similarities in the routines, as well as in word use, visual mediators, and endorsement, between the teacher and the student language, as well as between the two language settings. Limitations to this study, as well as the role of talk in the mathematics classroom, are discussed.