This paper claims a central role for school leaders (principals or head-teachers) in the enactment of social justice policy in schools, who act as key agents or 'gate keepers' for what counts as social justice in their contexts of practice. Social justice means different things in different contexts depending on where leaders -- who use policy as an opportunity to advance what they think is achievable within the limits of available resources -- are positioned in the field and how that defines their stances. Drawing on qualitative data generated through in-depth interviews with ten secondary school principals in two Australian cities, the paper analyses the engagement of school leaders with nationally prescribed equity-related policies. Our analysis shows that, depending on the institutional ethos and resources of schools and their own social justice dispositions, school leaders tend to take different stances towards nationally defined equity agendas. Their responses range from compliance to compromise to contest. The paper suggests that doing social justice in schools can never be unilateral, as policy documents suppose, but is characterised by context-informed policy translation, mediated by a range of interactive forces and interests.