Have you contactd the police about the anti-social behaviour towards you and your household? That is seperate to the school so it shouldn't matter if the school pooh-poohs it: this is no longer "just some children who don't get on" but it is a gang of ferral children verbally abusing adults and very young children. The police don't have to get in touch with the DREADFUL school about this to find "fault" or have your children blamed: THEY are the problem in this case and NEED a criminal record (IMO).