Yup, I remember those bus drills. Basically we got on a bus, got a lecture about how riding the bus was a privilege, not a right, how we should all wear our seat belts (HA!), etc, then went out the back door. Everyone had to go through it every year, even high school seniors, most of whom wouldn't be caught dead on a school bus. At least it got us out of gym...
Back in middle school, we had teachers who would oversee bus boarding at dismissal time. They would get on the bus every day to make sure we were all being good boys and girls and wearing our seat belts.
They must have known that the instant the bus pulled away, the seat belts came off.
We had a tornado drill once too, y'know, because tornadoes are so common in the Northeast.