From 1948 the World Health Organization expected child hygiene to include mental health. This article discusses the way school doctors adapted their activities and concerns accordingly in the mid-twentieth century in an agrarian-industrial area of the Netherlands. In spite of an improvement in pupils' physical health they shifted their attention only to a limited extent towards mental health. Nevertheless, it became an important aspect of their work, as they stimulated activities they conceived of as promoting both physical and mental health, such as gymnastics and swimming. Their key interest concerned mental deficiency and the promotion of special schooling. In this respect they played a very active role, to the extent of producing "feeblemindedness" and learning disabilities. At the same time the school doctors clung to their traditional ideal of supporting the school's effectiveness by trying to reduce possible dangers threatening pupils' learning capacity and, increasingly, their mental well-being.