Tolstoys, it sounds like your children's school(s) don't have adequate behaviour management policies. This is nothing whatsoever to do with corporal punishment.
In the inner city comprehensive my friend works in there are senior teachers time-tabled to walk around the school & remove miscreants who have been sent out of their classrooms for misbehaviour. There are several teachers time-tabled to do this every single lesson.
The children are then deposited in another classroom, supervised by more senior teachers, & their behaviour is followed up - there may be detentions, parents are contacted etc. It takes up a lot of time but means that students who want to learn are able to do so, & the school has been judged outstanding in terms of student behaviour.
I've taught in 3 different comprehensives too, & while none had a system quite as good as this, there were always behaviour policies & ways of dealing with difficult behaviour. I wasn't scared of parents (except the one threatening one I had to deal with ONCE) & the senior management teams certainly weren't.
I don't doubt there are schools out there with problems, poor leadership & little support available to teachers when it comes to behaviour management. But with the current Ofsted regime, there's really nowhere for schools like that to hide.
You sound very unhappy with your children's experiences. Have you spoken to the Head? What is the school doing to sort this out? Are you 100% sure that teachers are never allowed to have children removed from their classrooms, however badly they behave? If so, that's a major cause for concern, but it may be giving you a distorted view of what most young people (& schools) are like.