I'm very surprised at the way this thread has gone, because the usual way is to 'blame the teacher'
And there's some good points made about teaching your children respect. Sadly lost on a sizeable minority of parents nowadays.
I still believe that the majority of kids at school are at least willing to go along with the school, rather than fight it. But for every stirrer in a class, there'll be a 'fan club' of kids who won't incite trouble but will join in if they get the chance.
My technique was to pick out the roughest kid in the class, and give them hell if they stepped a millim