We used to have a 'mess with one, mess with all' policy (unofficial). Teachers would take pupils from the 'bad' classes to sit at the back of their 'good' ones, SLT would patrol, pop in now and then to ask whether anyone was stopping other people learning, and if so, remove them. Many of us would offer to support in frees-even if that sometimes meant taking some ba ones to sit in the hall copying from a textbook while you marked. Before any 2017 teacher starts moaning that this wasn't teaching and was depriving the little darlings- MOST of them didn't repeat this behaviour, and at least the rest of the class got to learn in peace. Parents were phoned (some cared-enough to help at least a little bit). There were always some who would keep trying it on, but this stopped the majority of the trouble.