This paper analyses the science of education that was formed in Ontario between the years 1910 and 1934. It is substantiated through the use of archival material such as curriculum documents, statutes, annual reports, the published proceedings of the Ontario Educational Association (OEA) and a close reading of the "Science of Education" manual published in 1915. This study examines how a science of education was defined discursively and put into operation through a series of political choices, institutional practices, and the agency of individuals in the education hierarchy. As a formative event in the history of schooling in Ontario, the emergence of a science of education in the early twentieth century defined the limits of a new terrain of pedagogic knowledge that sought to define a broad range of normalisations in teacher practice, pedagogy, methods, and the knowledge archive of the school system. This article considers how a science of education gave rise to new institutional forms and defined a terrain of knowledge that was used to identify and speak about students in new and different ways. (Contains 83 footnotes.)