Between 1946 and 1956, the Swedish Psychological and Pedagogical Institute (SPPI) organised several summer courses for the purpose of training teachers in intelligence testing. The aim of the courses was to make these teachers the first gatekeepers who would meet and direct the youngest pupils into ordinary classes or into special classes. This paper investigates the course leaders and the participants in these courses, as well as the content taught. It is argued that these testing courses are examples of a shift in assessment in education from trusting teachers’ ‘judgements’ of pupils’ skills and abilities to externally standardising the ‘measure’ of these merits. It is also argued that researchers and teachers were part of a larger change in the politics of IQ. SPPI’s role within this process was that of a new and modern institution serving society: making IQ testing a public familiarity and the stratification of children that often followed from it.