Teacher agency has been explored in many studies in different contexts, however research on supporting agency is somewhat limited. In this study, we aimed to support teacher agency in a collaborative inquiry-based in-service course developed based on the ecological model of teacher agency and earlier empirical studies. We conducted a study among 57 course participants to explore the potential impact of the course on participants' agency and investigated which role the motives to join the course had on participants' agency dynamics. Data were collected with questionnaires. The results showed that participants' agency was supported to some degree during the collaborative inquiry-based in-service training course, teachers' motives to join the course were somewhat related to professional agency dynamics.