A growing body of literature supports Inquiry-Based Learning (IBL) as a means to improve students' engagement and active participation in their education, and as a way to equip students for employment and social participation in the modern world. However, the introduction of an IBL curriculum raises significant challenges for teachers. This article describes the introduction of a middle years IBL program at a large public school in Victoria, and its development over three years, focusing on the impact of the IBL unit on the professional learning experiences of the school's middle years team. The project has generated significant shifts in the professional learning culture within the team. Its members have increasingly generated their own professional learning, and have disseminated their new knowledge within and beyond the school.