With an increasingly diverse population, Germany has been faced with the challenge of improving German academic language development and German as a second language (GSL) instruction in all subject areas. In all of Germany, approximately 20 percent of all students “have to learn mathematics in a language other than their first language,” (Prediger& Wessel, 2011). In Berlin, in particular, with 35 percent of students learning GSL (SenatsverwaltungfürBildung, Jugend und Wissenschaft, 2015), the implementation of interventions for improved academic language development and GSL instruction in all subject areas, and specifically in mathematics, is essential, but also presents teachers with a challenge. In addition, a crucial aspect of this context is the fact that recent studies have shown that many current teachers in Germany idealize the homogenous classroom (Morris-Lange, Wagner, &Altinay, 2016; Tillmann, 2008; Sturm, 2010). Thus, it becomes more imperative that future teachers are not only exposed to multilingual and multicultural teaching and learning environments, but that they are also given the skills to support all students in the changing educational environment. This research thus aims to examine Master’s level pre-service secondary math teachers’ subjective theories and their potential needs in integrating academic German language development and GSL into their math instruction, which can inform teacher training as well as later professional development programs. Pre-service math teachers’ subjective theories, including their beliefs, towards language acquisition and academic language development in the math classroom are important to instruction and student learning, as the teachers’ subjective theories tie in closely with what will actually happen in the classroom, thereby impacting students. The support of German language learners has been and will continue to be an important policy issue in the education field in Germany.