Educational concepts, such as enrolment, attendance, passing or failing students, school retardation, and school desertion, which made it possible to describe the course of children through the school system, went through a gradual process, beginning in the second half of the nineteenth century and throughout the first decades of the twentieth. In the early 1960s, a systematic set of categories was distilled, with "desercion" (school abandonment) occupying a central place. This paper analyses the development of these categories in the first half of the twentieth century, maintaining the hypothesis that toward the end of the 1950s, a new semantics was systematised for classifying children's course through school, which moulded and regulated the paths of schooling; the passage occurred from the psychometric and biotypological concepts of the 1920s to 1940s to concepts derived from economics and efficiency. The paper also analyses how this semantics, which originated in the school environment, spread to other social environments. For this purpose, it focuses on examples of the legal discourse aimed at regulating "juvenile delinquency" and proposes some reflections regarding the conceptual passages between fields. (Contains 6 figures and 63 footnotes.)