Yelling isn't the only form of discipline. There's withholding privileges. There's physical restraint even. Without cooperation from parents, school staff can't really do either. A teacher I know tells me how some of the violent elementary school children just get put in a room alone when they are having an episode because that's all they are allowed to do. These children (under 12 years old) have sent teachers to urgent care with injuries, and the kids are let back to school not long after.
physical restraint and discipline addresses a symptom, not the cause — if discipline worked the US wouldn't have outrageously high prison population and recidivism rates
The US justice system isn't discipline. It's punishment. Discipline isn't just giving consequences for actions, but it's also giving tools to choose better actions.
On that I agree, but specifying "discipline" for the average person often means punishment only. This is why the prison system is the way it is... no one wants to pay for things that benefit the prisoners, just the punishment.
