This chapter examines the ways in which data collection processes simplify and abstract complex phenomena into numbers, a process of reduction. It then explores this reduction by examining the effects and impacts of Baseline Assessment's use of simplified data in primary schools. The chapter considers the problematic nature of such reduction, and the problems of accuracy it creates. It explains the negation of English as an additional language (EAL) children's competencies in their first language through the assessment; the further narrowing of the curriculum; and the problem of assessing children of different ages. Baseline Assessment's hyper-positive scientific paradigm required the production of a single number, and that the three Baseline Assessment providers had to construct binary 'yes' or 'no' responses to a series of statements. The chapter reviews the issue of age more generally, and the emotional impact of attempts to collect data about 'development' with young children.