I'm not sure if this is true everywhere, but around here the only time the school bus has lights flashing is while its stopped to drop kids off or pick them up. If I get stuck behind it at this point, I just get off and walk my bike past the bus on the side where its letting people off. Then just keep on riding, the bus should never catch you again since it will make frequent stops. I would never recommend trying to pass the bus while its lights are flashing, you are bound to run down some little kid...