In recent years, schools have become increasingly multilingual, which must considered in mathematics teaching as the proportion of multilingual pupils is constantly increasing. Teachers ideas about teaching in multilingual mathematics classrooms, towards multilingual students and multilingualism are thus crucial to the students’ school achievements and identity information. Therefore, in-service teachers in compulsory school need to acknowledge multilingual pupils and language and cultural resources. Mathematics teaching needs to be adapted to a linguistic and cultural diversity in the classroom, where the students' different languages are used, and are seen as good resources.The method for collecting data relevant for this study: qualitative studies, which includes interviews and observations with active teachers in compulsory school. Relevant scientific articles were found in various databases, secondary sources, and also consultation with our supervisors and other course mates. However, the basis for this study is based on the empirical material that emerged in the qualitative interviews and observation, linked to relevant research.The result in this study are designed to provide knowledge about which aspects, teachers consider to be important, and knowledge development for multilingual students in mathematics education.