When I was at school, back in the 70's classes were well over 25, possibly closer to 30. The thing is, when does it come unmanageable for a teacher, 28,29? because there is not a lot of difference between 29 & 30. Why not just take away the extra children and make another class ? If you have 29 classes with 30 pupils, each class having to have an assistant, that's 29 extra employees, just take one pupil from each class to make another class of 29, get rid of the assistants and get 1 more teacher, or do you think they will struggle with 29, and if so, how many is manageable, 15,20, 5 ?