This article presents five case studies of grade six to grade eight science and mathematics teachers engaged in supported collaborative inquiry. The research focus is on teachers' growth trajectories related to their participation in professional learning communities supported through a professional development project. There were noticeably different trajectories in the teachers' progress through the inquiry cycle and a variation in the degree of collaboration in different professional learning communities. Some of the successes and challenges are attributed to the cross-grade, cross-disciplinary nature of the collaboration; others to teachers' existing relationships with each other prior to the beginning of this professional development project. The case study data indicate that dialogic inquiry grounded in classroom-based data is a key element in teachers' professional growth.