When I was in high school my bus driver would do the same thing and pull over and park till the kids settled down. At times we would pull over 4 times a day. Once the kids were so bad the driver took us back to the school.
Yeah, it was annoying, but the kids finally got the message...if you want to get home earlier sit down and BEHAVE!
The bus driver is in charge of many lives on their bus, they're driving a HUGE vehicle....they need to concentrate on driving and it can be hard to do that when the kids are extra loud and acting out.
Yeah, we would get taken back to the school or taken to the bus garage and they would unload us and call all of the parents to pick us up for find another driver whose mind wasn't frazzled.