The creation of international large-scale assessments in the 1960s and 1970s was inevitably a product of the movement of data. Large amounts of information about school performance circled the globe: first collected in individual schools, then aggregated at the national level, then sent to an international centre, and finally returned for further national analysis and dissemination. While the movement of data was a prerequisite for international testing, there was an inherent risk in how the work was organised. The concepts of data friction and precarious knowledge are used to describe how the pace of information transfer was slowed or how information was in danger of being lost as it circled the globe. The movement of data brought with it the double possibility of creating and destroying knowledge.