New data-driven technologies appear to promise a new era of accuracy and objectivity in scientifically-informed educational policy and governance. The data-scientific objectivity sought by education policy, however, is the result of practices of standardization and quantification deployed to settle controversies about the definition and measurement of human qualities by rendering them as categories and numbers. Focusing on the emerging policy agenda of 'social and emotional learning and skills,' this paper examines the practices of 'objectivity-making' underpinning this new field. Objectivity-making depends on three translations of (1) scientific expertise into standardized and enumerable definitions, (2) standardization into measurement technologies, and (3) the data produced through measurement technologies into objective policy-relevant knowledge, which consolidates a market in SEL technologies. The paper sheds light on knowledge-making practices in the era of big data and policy science, and their enduring reliance on the precarious construction of objectivity as a key legitimator of policy-relevant scientific knowledge and 'evidence-based' education governance.