This is a book about knowledge on and in education. The focus is on numbers—on how numbers shape our understandings of education, its dynamics, practices, operations, goals and missions. Important are the comparative powers of numbers—how differences and similarities between kinds of people and performances are constructed by numbers, over time and over places. Numbers appear to be neutral and precise, but like all symbols (such as letters, flags, etc.), the relations between numbers and what they represent are to be socially produced and learned, and the techniques to translate the one to the other (the symbol to its representation), such as statistics, are built on specific systems of reasoning. Numbers say little as such, but as they have come to be powerful representations of the modern world, shown in tables, diagrams or percentages, they are today also highly embedded with what is, and is not, of value and importance. Numbers are not only tools for analyses, but also highly performative, as they are framing our thoughts and conceptions of things. If there were a modern purgatory, it would be a spectacle of numbers that translated into such things as diagrams and regression lines showing dramatically where we are and what to expect, fear or hope for. Numbers make us read the world in taken-for-granted terms of progress and crises, ups and downs, differences and similarities. From where, and how, do these powers of numbers come about—and what are their premises and preconditions as they have come to play a key role in large-scale assessments and other forms of science-based policies and governance?