Research is an integral part of the UCL-led National Professional Qualification (NPQ) programmes. This is the fourth report in a series of research publications from the UCL Centre for Educational Leadership-led longitudinal study "The Impact of the Early Career Framework and NPQ Programmes on the Work Engagement, Wellbeing and Retention of Teachers and School Leaders." The purpose of this mixed methods study, which includes surveys of individual participants and case studies of 20 primary and secondary schools, is to assess the extent to which (and the ways in which) teachers' and school leaders' learning experiences on respective NPQ Senior Leadership (NPQSL), NPQ Headship (NPQH), and Specialist NPQ programmes influence their workload, wellbeing, and decisions to stay in teaching, move schools, or leave the profession. Evidence shows that the positive impact of NPQ learning is not achieved in isolation from the environments in which teachers and school leaders work, and thus points to a major source of the retention solution: the school organisation. Results supporting this observation may not appear new, but they reinforce important knowledge about teacher development and retention, nevertheless. As schools continue to face retention pressures, it is imperative that they are supported to have the capacity and resources to prioritise and nurture wellbeing as a central driver of professional effectiveness and long-term workforce sustainability.