!! YELLOW MEANS PREPARE TO STOP !!
The yellow lights on top of the school bus are to advise vehicles the bus is approaching a bus stop and is going to stop within 100 to 300 feet of activation. Traffic around the bus must prepare to stop at this point. This is NOT the time to speed up and go around the bus. 

!! RED MEANS STOP !!
The red lights on top of the school bus and side stop arm are advising drivers that the bus is stopped and loading/unloading passengers. Traffic around the bus is required to stop. If a patrol officer observes a vehicle passing a stopped school bus with the red lights flashing and stop arm deployed, the driver of the vehicle will be cited.