That was abuse. There is a line between telling him to knock it off and actually choking him-if she could not handle driving that bus, she needed to be on the "normal" bus, where kids would be just as likely to throw a can at the back of her head... except, they would giggle about it afterward.
The fact of the matter is, she is just the driver. She likely has no clue how to deal with this situation, and that is exactly why the monitor was supposed to be there. She snapped and lost her cool, and you just cannot do that when dealing with children-especially when they aren't your own.
I have no clue how I would have handled the situation... but ya know what? There's a reason I'm not a bus driver, lol, and it's because I don't know how I could handle it in general.
Here in our area, we've had things like this happen, and there is a way they always deal with it. They pull over to the side of the road and try to calm them down by talking first, and if that doesn't help, they call up the bus company or school and tell them where they are at, and that the parents need to come pick up their child from the bus. That is all there is to it. They just stand outside of the bus while the kiddo is inside (keys out of course), and wait for the parents.
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Sorry about the incredibly long post...
"I enjoyed the meetings, too. It was like having friends." -Luna Lovegood