This thesis aims to explore the mathematics achievement of second language immigrants in compulsory school as they continue their schooling in Sweden. Specifically, the thesis aims to generate more knowledge about different sub-categories of second language students, namely newly arrived immigrants, early arrived immigrants and other second language students in compulsory school. The data in this thesis consists of students’ responses to test items and thus mainly contains mathematical symbols, essentially numbers in different representations, written by the students. Doing so, this thesis problematizes the concept of second language students in mathematics in two aspects. One aspect is to assess the first and second language students’ achi...