The concerns over school segregation have gained salience in Finland in the last two decades, paralleling the discussions elsewhere in Europe. This article examines from the pupil perspective, how school segregation and school selection are 'lived' in a lower secondary school in the metropolitan area of Helsinki. Using the concept of borderwork, I examine the hierarchies produced by the divide between selective, mixed and non-selective school class groups in pupils' social relationships, and how these hierarchies intersect with social class and racialization. The article is based on interviews of altogether 46 pupils in the 7th and 8th grades (aged 13-15). I argue that school class groupings are a strong organizing principle in pupils' social relationships, and that pupils' borderwork narratives on selective and non-selective school class groups build on and help consolidate the social class-based and racialized differences between the groups.