Teachers in mathematics classrooms where the language of instruction differs from students' first language face competing demands regarding mathematics and language teaching. In this study, I conducted an analysis of genre of teaching episodes to examine how a teacher in a Spanish immersion third-grade classroom in the US responded to those demands. Findings indicate that the genres on which the teacher drew are associated with mathematics and with language classrooms, in addition to general genres that can be found in either classroom. I argue that the teacher's awareness of school demands and of students' needs influenced how genre-switching unfolded. I discuss how genre analysis adds to conceptualisations of mathematics and language as integrated in CLIL classrooms. [For the complete proceedings, see ED606531.]