It isn't only the teachers who are under stress.
Its the pupils who suffer as well, a disruptive pupil can hold back a whole class and affect their education.
Kids who mishaved in class used to get caned and the problem was sorted, nowadays it dealt with by exclusion, but even that is under threat of being outlawed by the liberal establishment, most of whom don't have to work in problem schools.
Kids who used to go special schools which could cater for their needs are now sent to regular state schools.
A lot of this kids can't cope in a normal school environment and so they start disrupting the rest of the class, they tend to be quite difficult to deal with due to their problems, if they end up being excluded the parents complain that their kids are being picked on.