DS is 5 and I will freely admit can be a ratbag if overtired or coming down with something BUT at home he understands that he does as he's told or there are consequences (time out, loss of TV or tablet time, loss of a treat for example). Recently DH has been called a couple of times to pick DS up during the school day and bring him home early because he's been slapping or kicking, or running away from staff.
After a couple of incidents of either being told about this behaviour at home time or being asked to pick him up, we were properly clear with him at home that hitting is unacceptable, you need to do as the teachers ask etc. and he had a couple of evenings of no cartoons, no story at bedtime etc. However, talking to him about why he's been so naughty at school he says he's confused - and why? Turns out he's being told that he can't hit, but another child in the class is hitting him and not being disciplined for it - DH checked with one of the teaching assistants and they don't use the word naughty, or unacceptable, or actually do anything to provide a consequence for poor behaviour. Literally all they have is a happy sun or a sad cloud, and DS has recently been sent home with DH being told he's been hitting, but having been put in the happy sun during the day
My usually happy little boy is quite obviously worried after the last couple of weeks and I'm getting quite cross with the school seemingly having no policy on discipline but expecting the parents to be able to magically convince kids to do as we say, not as the teachers allow them to do...