This study analyses the collaboration between principals within four Flemish school federations (voluntary collaborative networks between either primary or secondary schools). Interview data from principals were analysed using a micropolitical perspective. A central idea in micropolitical theory is that organization members' actions (and sense-making) are largely driven by their interests. As such this perspective allows to understand how principals' interests influence how collaborations within federations work out in practice. In three federations, we found an alignment of principals' interests that stimulated a collaborative dynamic, which eventually contributed to improvement of the federation. Moreover, it also enhanced principals' professional development. In the fourth case, however, such dynamics were absent due to a conflict of interests between the federation and one member school. Because one school felt the federation threatened its educational identity and mission, it almost completely withdrew from the federation. Thus, we conclude that principals' balancing of interests plays an important role in the development of collaborative relationships and practices within school federations.