Since 2000, girls' education has been an increasingly high-profile concern in international development policy. At the same time, there has been a trend towards the greater production and reliance on quantitative data, indicators and targets in national and international education policy. Scholars have raised concerns about the rise of 'performance-based' approaches to accountability in education, and potential counterproductive effects of this for social justice and equality. However, few studies have explored how this trend plays out in practice within international organisations, particularly in relation to the heightened focus on girls' education. This paper explores the implications of the increasing reliance on quantitative measures for policy actors and draws on a set of interviews with key stakeholders working in organisations concerned with gender and education to explore their divergent understandings of accountability processes. The paper concludes by reflecting on the prospects for a transformative approach to measuring gender equality and girls' education.