Prior research has shown the importance of collaborative culture as well as teacher job satisfaction and commitment in navigating complex school improvement processes. This study investigated the relationship between collaborative culture, affective commitment, and job satisfaction of teachers taking both collaborative cultures in the entire school, as well as in informal subgroups, into account. Survey data of 760 teachers, nested in 136 subgroups and 13 secondary schools, were analyzed using multilevel path analyses. Results show that collaborative culture in the informal subgroup is positively related to teachers' affective commitment and job satisfaction and that affective commitment is a mediator. The collaborative culture at the school level was not a significant predictor. School leaders need to be aware that there are, to some extent, subgroups within the school which develop their own collaborative culture through social contagion processes which impact job satisfaction and affective commitment to a greater extent than the school-level culture.