They just get rid of them. Relationships between pupils and teachers at the PRUs are based on mutual respect, a concept that was alien to pupils before they joined. A view that is echoed by everyone and something they value as key to their progress. They need permission from a higher level to take time to do that. Class sizes at the PRUs are a fraction of normal classes with just seven or eight pupils in a lesson.
Smaller classes ensure pupils get individual time with the teacher.
Pupils feel they can ask for help without being seen as disruptive and a burden. They are given the support and attention they need to study effectively. In my old school I was disruptive. They give you more help here and they explain things to you properly. Many of the pupils discover they are capable of much more than they thought possible.