Here is a question from DMV Manual
Q: What does it mean when a school bus is stopped and its red lights are flashing
1) You may pass if no children are on the road.
2) You may not pass while the red lights are flashing.
3) You may pass if you are facing the front of the bus.
4) You may pass if it is on the other side of a divided highway.
The answer is
2) You may not pass while the red lights are flashing.
When a stopped school bus flashes its red light(s), traffic that approaches from either direction
must stop before it reaches the bus.
You should stop at least 20 feet (6 m) away from the bus.
You must stop for a school bus even if it is on the opposite side of a divided highway.