This article offers insights into the challenges and complexities of accredited national professional learning programmes that are collaboratively designed, led, and delivered. The article is framed within theoretical perspectives concerning large-scale system change, highlighting the importance of inter-professional relationships and joint work in establishing shared goals for educational improvement. Drawing upon two accredited national programmes, in Scotland and Wales respectively, the article considers the intentions, processes, and outcomes of professional learning at scale. It focuses on the highly complex network of influences, in the system, that shape the way that professional learning, at scale, impacts upon learning and teaching. The article explores the challenges of implementing an accredited national professional learning programme and outlines some of the complexities of delivery, assessment, and quality assurance. It highlights the power and potential of national professional learning programmes for the individual, the school, and the system. The article touches upon the role of stakeholders in the design of the national programmes. The article concludes that the intersection of leadership, collaboration and a shared commitment to capacity building is the key to the overcoming the complexities of securing effective professional learning at scale.