To reach the goals of communication and reasoning in mathematics in upper secondary school, students need to talk about mathematics but sometimes this is not as easy to achieve as it first seems. In this paper, an initial analysis is provided of tasks and strategies from an educational design research project promoting student-to-student interaction. The data include students’ interactions and perceptions on working with mathematics in groups from the first of three cycles. They are analysed and discussed in relationship to the choice of analytical tools, means of support and tasks for the remaining cycles