This paper analyses the experiences of English primary school leaders who perform critical roles in interpreting government policy and navigating the landscape to design relationship and sex education (RSE) for their pupils. It considers schools as sites of political contestation and educators as policy actors, the voices of whom are often absent in the literature about RSE. Drawing on Peter Morriss' theory of power, the paper considers how primary school decision makers utilise their epistemic abilities to advance their policy preferences and how structures of authority and legitimacy energize and constrain them in their policy-making work. The findings suggest a paradox in power: while the national government has delegated decision-making about RSE to individual schools, it has simultaneously failed to uniformly equip schools to make appropriate policies about RSE and enabled parents to deny schools' credibility and authority as leaders in RSE.