In Jomtien in 1990 and again in Dakar in 2000, world leaders committed to the measurement and improvement of learning as part of Education for All. Yet clear, actionable metrics, particularly in the early grades and in the poorest countries, would continue to elude the sector. This paper reflects on the development and impact of the early grades reading and mathematics assessments, open-source tools applied in more than 60 countries and 100 languages. Case studies illustrate the promise and pitfalls of working at national scale, while summary results from 10nationally representative studies document the scope of the crisis in early learning. The authors conclude with reflections and aspirations for placing country-driven learning assessment at the centre of post-2015 goals.