You do not have to stop for a stopped school bus that is loading or unloading children if:

On a two-lane road, all traffic must stop and remain stopped as long as the red lights near the top of a school bus are flashing and/or the stop arm on the left side of the bus is extended. On a highway with two or more lanes traveling in each direction, oncoming traffic is not required to stop when meeting a school bus.
DMV Writen Test