This article presents one of the few qualitative studies to empirically examine the collaboration between private sponsors and principals in the context of England's academy schools policy. It uses the concept of boundary-work to illuminate the multiple dynamics involved in the collaboration between principals and business sponsors. By analysing qualitative interviews with principals and sponsors from a local authority case study the article reveals the working relationship between these actors to be characterised by three boundary-work practices: drawing, negotiating and contesting boundaries. These practices are described before exploring their implications for existing understandings of England's academies policy. This analysis directly answers calls in the literature for in-depth case study research which explores the collaboration between academy sponsors and principals, and the article's interpretivist approach to boundary-work is shown to be a valuable theoretical approach which has received little attention in studies investigating the role of private actors in education. The article concludes by advocating for more studies of education policy to use boundary-work as a lens through which to understand the role being played by new actors in education, and argues that this perspective would be particularly valuable for examining the context of England's increasingly diversifying schooling landscape.