Language support for multilingual learners plays a major role in classrooms today. Because there is a need for facilitation of academic language in all subject areas of the classroom, all teachers are expected to have the ability to scaffold language acquisition in their subject area. The development of special teacher training programs in the field of second language teaching which help pre-and in-service teachers to acquire the abilities to facilitate their students’ academic language learning is seen as important in Germany as much as internationally. This article describes the role of German as a Second Language (GSL) in German university teacher training and a theoretically and empirically validated competency model. Furthermore, this article presents not only the description of a GSL preservice teacher training in Berlin universities but also the evaluation results. Future teachers’ GSL competencies were measured using the standardized DaZKom test at two measurement points. Students showed significantly higher skills after attending GSL training. Students who study German showed higher skills than students who do not and students who study a foreign language also showed higher skills than students who did not. Master students had significantly higher GSL competencies compared to bachelor students. © 2020 selection and editorial matter, Svenja Hammer, Kara Mitchell Viesca, and Nancy L. Commins; individual chapters, the contributors.