Teacher professional learning is widely accepted as a mediating factor for enhancing student outcomes. While many teachers across the world engage in professional development (PD) to enhance their professional learning, what is 10 less evident is how to support that learning to result in change following teacher PD. Acknowledging that not all teacher PD needs to result in new practices and change this paper focuses on a transformative model of PD, focused on implementing and sustaining change. This paper offers evidence of successful implementation and sustainability of practices by drawing from in-depth 15 semi-structured interviews with teachers and principals in five Irish case study schools. It reports on the Systemic Factors to support implementation and sustainability of change: Support, Initiative design and Impact and Teacher Agency. Implications are drawn for bridging the gap between knowledge and practice or teacher PD and change within schools.