This article examines the construction and design of literacy attainment data in the English school system in two different historical periods: the 1860s and the 1950s. These periods represent contrasting moments in the history of education in the UK when school structures and the governance of education varied, as did the design and interpretation of literacy attainment data, their relationship to pedagogy and the curriculum, and the administrative purposes for which they were deployed. By paying attention to the relationship between the form the data took and their mobilisation in administrative, professional and public discourse, this article will challenge current assumptions about the primacy of numerical data and the certainty accorded the information they encode. Studying the role numerical data played in shaping education in the past reveals tension points between data, discourse and social contexts that highlight the peculiarities of contemporary uses of literacy attainment data and their current role in bringing policy and pedagogy into the same space.