This chapter begins with the analysis of research data with a deeper exploration of what 'datafication' looks like in schools and early years settings – its forms, practices, artefacts and values. It argues that data are an important part of the operation of power in education. The chapter provides a detailed discussion of the ways in which data disrupt and challenge established pedagogical practices, and the tensions between the necessity for school performance data and young children's emotional well-being and learning. It explores the impact of datafication on students' subjectivities. The chapter considers the role of school leaders as managers and interpreters of data, and the new roles and reliance created by datafication. It explains how data affect teachers' and students' every-day lives, their relationships to each other and their value within the school: the production of data-driven subjectivities in education.