Whereas previous studies on teacher collaboration have focused almost exclusively on improving teaching, this paper investigates collaboration in three highly important school improvement areas. Data for three collaboration networks were collected in four secondary schools in Switzerland in 2018 on teachers exploring new ideas on teaching (teaching improvement), teamwork (team improvement), and school organization (organizational improvement). Using social network analysis, we examined to what extent the collaboration networks overlap, how network structures differ, and what factors explain these differences. The results revealed substantial differences between collaboration in the three areas. This suggests that future research should examine collaboration from a multidimensional network perspective.