What students write is assumed to show their knowledge in mathematics, although they seldom are given the opportunity to learn about what a well written text can look like. Teaching mathematics should include to equip students with tools for functional writing in a cognitive meaning as well as a social. This study examines how students use representation when writing during problem solving. In addition, the quality of their texts is assessed with the social function in focus. The participating students have through action research taken part of teaching about the Singapore model method. By analyzing pre and posttests a change in their writing was made visible, a change that resulted in improved quality. The model method is well known as a strategy for problem solving, but this study shows that it also can be used to present information to a reader. Therefore, it is suggested that the model method can be used in mathematics teaching to improve students’ writing skills in a social sense. / <p>Matematik</p>