Escalating student diversity and increasing accountability in Australia have brought important ethical challenges for schools and their leadership teams. In aiming to balance the ethical principles of ‘the general good’ and of ‘the individual good’, leaders are finding that they are now dealing increasingly with issues of equity and fairness as these relate to assessment. Research evidence indicates that when assessment systems use the same data to hold to account the students who are being assessed as well as hold their teachers to account then unintended consequences and damaging effects will result (O’Neill, 2013; Nichols & Berliner, 2005). In this paper we draw on interview and observation data from an ARC Linkage Project investigating how leaders ethically promote equity and improvement in learning outcomes through their use of student achievement data. In the analysis of the research data consideration is given to structural issues of socio-economic status, gender and ethnicity. A view of education that is not just economic, but is also social, cultural and political, is adopted to analyse the emergent tensions and ethical dilemmas that confront leaders in the current reform context.