This seems bizarre to me. I've just spent half an hour comforting my just-turned-six year old who is in tears at bedtime. Apparently today a boy was naughty (messing about when he was supposed to be keeping quiet) and the teacher has told them they will all have to stay in at break tomorrow.
My child can't understand why she is being punished when she hasn't been done anything wrong. And neither can I! I do understand the principle of trying to use peer pressure but surely this age - five and six - they are too young. Is it common at this age?