The OECD's international education indicators have become very influential in contemporary education policies. Although these indicators are now routinely, annually published in the form of "Education at a Glance," the calculability upon which the indicators depend was an achievement that involved the mobilisation of a huge machinery of expertise, trust, pragmatism and other resources. This paper traces the ways in which varied constraints were addressed, interests translated, categories defined, classifications negotiated, frameworks agreed upon, choices made, methodologies established and protocols developed, as the indicators exercise moved from being nearly impossible to becoming routinely produced. Using resources from Science and Technology Studies (STS), it demonstrates that the work of making such assemblages is both instrumentalist and performative, and argues for an undertaking of critique as a moral enterprise.