This paper presents results of a cooperation which compares data of two different ethnographic projects. The projects were realised as singular ethnographic enterprises, but share a lot of ground. Both of the projects included fieldwork in age-mixed primary classrooms and focused on children´s interaction and peer-cultural relationships. Building on this shared ground we set out to explore how the comparison of data from two different projects could create a synergy. Our cooperation aimed at shedding new light on our interpretations and challenging preconceived notions. Developing foci of interpretation which transcended our individual projects gave us the chance to look at data differently as well as interpreting data which had not been analysed as systematically before. The paper will discuss how comparative perspectives were established, how these created new analytic lenses, and how we build new ground to theorize the pedagogy of age-mixed grouping. A focus will be on the methodological challenges and chances of a synthesis of ethnographic data.