Effective professional learning is acknowledged as a key lever to improve teacher practice. However, many studies report significant variation in the effectiveness of the types of programs on offer. Recently, there has been a move from the traditional single event, passive approach to more collaborative and ongoing forms of professional learning. Interestingly, researchers have paid little attention to understanding the experience of professional learning from the teachers' viewpoint. This research sought to develop this understanding by following the attitudes and behaviours of a group of secondary teachers as they participated in an ongoing professional learning program. This professional learning program tracked teachers as they participated in workshops and then applied the learning to their classrooms. Our results suggest five interacting characteristics that contributed to improvements in teaching practice. These findings underpin the development of a process model of professional learning, that we call the Iterative Model of Professional Learning (IMPL).