This article discusses how group supervision can be used to support the Continuing Professional Development (CPD) of those working with children and families in early years provision in England. It is based on research conducted in 2008 with a cluster of four Children's Centres in the West Midlands in England, UK. The research evaluated group supervision with 12 Family Support Workers (FSWs) and three managers, using Realistic Evaluation (Pawson and Tilley 1997) as the methodological approach. The research identified key mechanisms within the group supervision process: the professional contract, group working agreement, facilitation and size of the group. In addition, the research identified key features of the context, namely management support and group dynamics. This article will focus on the key mechanisms within the group supervision process, and the key features of the context, whilst providing a brief overview of the outcomes. (Contains 5 tables.)