This study aims to investigate students’ strategy use in performing problem-solving tasks about the measurement of a circle's area, and whether the students' individual strategy thinking develops during discussions about strategic choices in heterogeneous groups. The theories that are linked to this study are Strategy use, Heterogeneity, and Classroom norms. The theories about strategy use are about the student’s choice of strategies and about the students' understanding of the strategy they choose to use. The theory about Classroom norms indicates that teachers and other students influence students' mathematical reasoning and calculation. Finally, the theory about Heterogeneity, tells us how students' different knowledge levels, backgrounds and experiences influence the development of mathematics. The study was implemented in two classes from year six in primary school, where a total of four heterogeneous groups from these classes were created. The students had to individually perform three problem-solving tasks which involved calculating the area of ​​the circle. The students were taught different strategies for making these calculations and they could use any strategy. Students then discussed their solution strategies in groups before they had to solve the next task.  The results of the research show that the only relevant strategy used in the four groups was the multiplication strategy. The reason why the students used the multiplication strategy was directly connected to the classroom norms the teacher had presented. Therefore, students learned the multiplication strategy and they implemented it immediately without understanding why they calculated it in that way. Because the students only used one relevant strategy to calculate the area of ​​the circle in all groups, there was no exchange of strategies. There was, however, an exchange of experience. Since the students who used irrelevant strategies understood how other students solved the problem-solving tasks about the area of ​​the circle with the multiplication strategy. As a result of the discussions in heterogeneous groups, the students who used irrelevant strategies started using the multiplications strategy eventually.