This chapter shows how data make educational performance more visible, and how this increased visibility results in strategic responses from school leaders and teachers. It focuses on research data from our second project relating to whole-school responses to datafication, considering the range of reactions to a new policy, and processes of resistance, compliance and manipulation. The chapter focuses on data abuse, which is where data use in an accountability system can cause 'problematic consequences', which is distinct from data misuse, meaning the incorrect interpretation of data and the resulting inappropriate responses. It then considers the ways in which datafication produces new strategies and approaches, and also new tensions. The chapter shows how the 'reification of progress' demands different forms of data alongside summative assessment data, and the relationship between progress and prediction. It discusses the reminder of the power of visibility in neoliberal forms of governance, as summed up in Lewis and Hardy's phrase, the 'tyranny of transparency'.