This study investigates how pre-service teachers (PSTs) negotiate an understanding of which multilingual practices are legitimate in mainstream education in Norway. Data were collected through seven focus groups with 24 PSTs participating in their first field placement. I designed three fictive vignettes about multilingual students in mainstream education, and these were introduced and discussed in the focus groups. The analysis of the PSTs' discussions of multilingual practices in mainstream education drew on Ruiz's framework of language ideologies and Bakhtin's concept of heteroglossia. The analysis shows how the PSTs were concerned with the needs of the class, of the teacher and of the multilingual students when multilingual practices were introduced to mainstream classrooms. The PSTs drew on different language ideologies to determine which multilingual practices were legitimate. The results indicate that the PSTs considered multilingual practices to be legitimate if they did not compromise group work nor challenged Norwegian as the language of instruction. However, the results also show a potential to work with PSTs in order to develop awareness of their own heteroglossic language ideologies. This study suggests that teacher educators can use focus groups to achieve this goal.