Integrated Leadership Development Programmes (IDLPs) have become increasingly popular in recent years. These programmes combine different elements such as 360° feedback, experiential learning, group coaching, executive coaching and action learning, over extended periods of many months. Very little independent research exists to show how effective they really are and this longitudinal study helps fill that gap in knowledge. Based upon a case study of 530 managers in a UK-wide public sector organisation over four years, the study uses a mixed methods approach. Findings confirm that ILDPs are highly effective and also identify current best practice design. The research also demonstrates that increasing the amount of coaching leads to increased learning transfer and retention.