In the Swedish compulsory school today, at least 140 languages are spoken by students—a situation entailing both challenges and opportunities for teachers. This paper presents an investigation of how teachers are prepared to meet these students, who may be either newly arrived and fairly new speakers of Swedish or students born in Sweden with other languages at home. The focus is on how ideological and implementational spaces for supporting linguistic diversity in the classroom are created and accessed in pre-service teacher training. First, the national curriculum for the compulsory school as well as the education plans and syllabi of obligatory pre-service teacher training courses were analysed, with an aim to identity spaces for multilingualism in these educational policies. Second, a study of teacher educators and pre-service teachers from four national universities was conducted, with semi-structured interviews to elicit their perspectives and experiences. The results reveal a lack of explicit emphasis in the national curriculum on students as a diverse population, with ideological spaces for multilingualism only implicit. Likewise, teacher educators and pre-service teachers generally feel that preparation for how to support linguistic diversity in the mainstream classroom is deficient in teacher education and could be afforded greater attention. With a lack of clear directives in policy and a lack of focus in pre-service training, there are risks of inconsistent interpretation and implementation of practices supporting linguistic diversity in the compulsory school.