The majority of European educational systems regard the provision of high-quality language and learning support for students with immigrant background as the greatest challenge and consider separate language support classes as 'the solution' to the educational disadvantages these students face. Austria recently implemented separate language support programmes ('German language support classes and courses = GLSCC') for students with beginner-level German language skills. There is a growing body of literature which indicates that separate language learning programmes result in lower academic achievement of students with immigrant background compared to inclusive programmes. This study presents teachers' perceptions (n = 1.267) of positive or negative effects of the GLSCC in Austrian schools. With regard to positive effects, teachers view the GLSCC as an opportunity for individualised and differentiated instruction. However, many teachers reported negative effects in the social dimension which refer to social exclusion and processes of othering. Furthermore, the findings indicate a variety of deficiencies on a didactic (e.g. students miss content in other subjects) and organisational level (e.g. lack of adequate rooms) and indicate a strong need for improved teacher education and training to teach heterogeneous classes.