When a school bus is stopped and the red lights are flashing on the bus you must stop and remain stopped and cannot pass the school bus even when the stop sign is not out.
When a school bus stops and starts the flashing red lights it means that they're about to deploy the stop sign but if the school bus is stopped and no red lights are flashing and the stop sign is not out you can usually pass the school buss and go around the stopped school bus.
But be aware in case someone is crossing the street anyway and school buses are now adding cameras to their stop signs to catch motorists who are illegally passing the school bus when the stop sign is out.