The aim of this article is to discuss and problematise issues related to conceptual approaches to differences among children in the world of school education. The article is based on results from a Swedish study on categorisation of schoolchildren’s ‘problems’ from a historical perspective. Its central questions are: ‘What concepts are used to formulate children’s various educational needs, and how can these concepts be understood?’ Supported by an ecological analysis model, complex situations in the categorisation and problem-solving process are clarified. Using terminology to refer to pupils’ diverse abilities and needs involves aspects of categorising. An understanding of how this works may bring more profound knowledge of obstacles to children’s learning. The categorisation process illustrates effects both at individual level and more generally. Categorisation may be regarded as a useful practice for understanding children’s differences better, and thereby finding the best ways of responding to them. However, categorisation based on abilities and needs also adds a challenge to the important idea of inclusion. The article discusses categorisation as a basis for educational problem-solving and the implications of categorising children’s varying abilities and experience of school education. The theoretical premises enhance understanding of the dynamic nature of terminology usage, and thus future prospects of meeting challenges that may arise, in schools.