This article discusses the central issue of the transition to preschool. Individual semi-structured interviews with school professionals and parents in the Brussels region revealed that this issue is crucial for the well-being of young children, from both an educational and a social perspective. We discovered that the education system works under the assumption that nearly every child has attended daycare before entering preschool. This has serious implications since using these services, which help to prepare children for preschool, is socially differentiated. Children who have to cope with their first socialisation outside the family environment and their first encounter with the school environment at the same time face many problems. Not only does it define their first school experience; more importantly, it contributes to shape their entire experience of preschool, with potential long-term harmful effects. The article discusses the corresponding implications for the school system and puts forward recommendations.