Results of (inter-)national large-scale student assessments tend to show that students with a migration background have lower competencies. This correlation between migration and student achievement has been proven for many countries and for various stages of the educational system. The reasons for these findings are particularly seen in a lack of students‘ competences in the language of instruction. Since 2014, 33 secondary schools in North Rhine- Westphalia have been taking part in a project attempting to strengthen or rather implement “language-aware” teaching in schools. To better meet the needs of an ever more diverse student population, the project aims at sensitizing school leaders and teachers to the issues of multiculturalism and multilingualism and enhancing their skills for fostering students‘ competences in the language of instruction. In this paper, we draw on findings from the evaluation of this project. Here, 46 school leaders, 487 teachers, and 2,526 students from class 6 were interviewed. All of the schools in the sample show a high percentage of students having a migration background and/ or with low scores in linguistic proficiency assessments. The schools work together in one school leader network as well as in six regional school networks and are supported by network counsellors. The results from the initial survey showed that teachers lack competences in including students‘ first languages in their teaching. They tend to treat all students equally rather than to pick out students‘ languages and their cultural background as a central theme in class. Moreover, feedback concerning students‘ lan-guage competences, as well as measures to enhance their vocabulary could be developed further.