I was a sub teacher for a bit right after college. "children's village" had a hard time getting people to fill in and called me back a few times because I didn't scare quite as easily as some others. I learned the trick was to tell the whole class that they were about to get free time restriction and i'd tell the guards that somebody stole a pencil because larry, moe, or curly wouldn't act right...
I don't care how many gas station attendants a teen has killed, when he's faced with 30 other teens angry about the thought of getting their cavities searched and being put in lockdown for another full day, he's gonna settle down a bit.
It was probably a little unethical... but once or twice it was either that or get into a physical confrontation when one of the boys wanted to flex. I'm not a big guy and I did not fancy the idea of having a couple of young murderers gang up on me. No guards, just me in a locked room with 30 young inmates.
Still, that was a lot less stressful than handling the girls' classes. Even with a chaperone in the room, some of the underage girl inmates just wanted to get ... grabby.