International organisations' (IOs) legitimacy in global educational governance is commonly seen as a function of their regulative or normative power. By contrast, this paper stresses the increasing importance of scientific research and policy-relevant knowledge and its strategic production, dissemination and transfer by IOs. The article examines knowledge work at OECD, UNESCO and World Bank based on novel data from publication analyses, archival work and a number of interviews. Drawing on sociological institutionalism and constructivist international relations scholarship, this study is interested in the rationales, resources and capacities for knowledge production, the strategies of dissemination and transfer as well as the implications of science production for IOs' position and relevance in global governance. Findings emphasise the authority of science as the primary source of legitimacy -- and even survival -- in an increasingly crowded and competitive field of global education governance.