Countries world-wide face the task of integrating students with various linguistic resources and ways of living into their educational systems. The specifically German institution of vocational schools in Germany is complex and, especially in the subject of German, presents teachers with the challenge of ensuring language and subject learning with a diverse and linguistically heterogeneous student group. Studies show that all students at vocational schools need targeted language education in order to be able to cope with the demands of vocational school and training. However, teachers with a grounding in German as a Second Language (GSL) are the exception, yet. And we have only little empirical evidence about the professional activities of teachers at vocational schools who have acquired further training in GSL. With an online survey among N = 81 teachers at vocational schools in Northern Germany, we are addressing this gap. Our results show that there is a connection between their professional training in GSL and the degree of their awareness for the linguistic side of vocational teaching and reveal a comparison between teachers with and without a background in GSL reveals differences in the approach to vocational language and vocational learning. This is twofold: teachers with in-service training in GSL take language issues more into account in their text-based lessons as well as support the writing and the writing process of all of their students consistently. However, teachers at vocational schools do share a general feeling of not being sufficiently competent when dealing with multilingual classes. In our article we discuss implications for teacher education and teacher training for German vocational schools to make them stronger in preparing for lifelong learning in the 21 century.