Although migration itself is not a new phenomenon, the rising numbers of refugees in Germany and Europe are influencing the population composition leading to greater diversity within our society. This particularly affects school systems, as a great number of refugees are of school age and have to be provided with adequate schooling. In this paper, we discuss how the German education system, in particular in the city of Hamburg, deals with the schooling and integration of refugee students in what are called International Preparatory Classes. We describe a research study, which is examining what aspects influence teaching practices in mathematics lessons in these classes for refugees. The study investigates how teachers in these classes design their lessons from a mathematical and a linguistic perspective, how they deal with the task of providing refugee students with adequate instruction and how students experience mathematics.