This article explores the tensions between medical and pedagogical professionals involved with the classification and selection of pupils for the special day-schools for “feebleminded” children that were established from 1900 in the Netherlands to promote compulsory mass schooling’s efficiency. These are set against the increasing influence of child sciences, including the new technique of intelligence testing. These schools were meant for educable learning-disabled children, the classification of whom involved a child’s (ab)normality and (in)educability. The article discusses the categories defined and labels inscribed on children with learning disabilities. These focused mainly on a child’s capacity to communicate and learn to adapt to society, as the special schools aimed to educate productive members of society. In spite of the recognised merits of the schools, theorists turned out to be most concerned about undue placements of not “essentially backward” children, who would benefit more from educational support in a regular school. The selection and admission procedure of the schools was standardised by the introduction in 1920 of intelligence testing as part of a developing scientific assessment culture, which for want of psychologists and despite the headmasters’ professionalisation continued to be dominated by the medical profession up to the Second World War.