This article explores the role of psychiatry in the sorting of schoolchildren in Denmark, Norway, and Sweden from 1920 to 1950. Whereas the role and rise of educational psychology and IQ-testing in the differentiation processes in schooling have been examined through earlier research, the role of psychiatry in the interprofessional collaboration has so far been largely unexplored when it comes to the Scandinavian case. In line with Michel Foucault, the article regards these professional efforts as part of the biopolitics, where psychiatry amongst other disciplines engaged in the development of means to involve strategically in the life of schoolchildren and their families, as part of shaping the future of the population. We argue that psychiatric sorting activities related to schoolchildren did not solely take place through IQ-testing in schools, but involved classification of children through a range of measures in various settings. We further argue that these processes took place due to local agents and initiatives in a broader context of interprofessional collaborations between psychiatrists, psychologists, and teachers, rather than top--down processes initiated by the state. The analysis in the article draws on different sources of the period: journals, articles, and monographs from the key-agents of the period.