This study investigates the impact of collaborative reflections on teachers' inquiry teaching practices and identifies supportive actions relating to their professional development. Three science teachers in the same elementary school worked as a cooperative and collaborative group. They attended workshops and worked collaboratively through observing colleagues' teaching practices and discussing with university professors about their own inquiry teaching. The pre- and post-treatment classroom observations and comparisons of their teaching reveal that the three teachers were more focussed on asking inquiry-oriented questions in the post-treatment teaching. With additional qualitative data analysis, this study identified supportive resources of professional development. Workshop training sessions and sample unit served as the initiative agent in the beginning stage. Discussions with peers and reflective observation of peer teaching acted as a facilitative agent. Finally, student responses and researchers' on-site visit comments worked as a catalytic agent for their professional development.