"The ONLY time you can pass a stopped school bus with it's red lights flashing is when you are traveling in the opposite direction AND there is a RAISED median between you and the school bus. A painted line separating traffic is not a raised median island. It must be a raised barrier of some kind."
CA driver's Handbook :
When the bus flashes red lights (located at the top front and back of the bus), you must
stop from either direction until the children are safely across the street and the lights stop flashing. The law requires you to remain stopped as long as the red lights are flashing (CVC §22454). If you fail to stop, you may be fined up to $1,000 and your driving privilege could be suspended for one year. If the school bus is on the other side of a
divided or multilane (two or more lanes in each direction) highway, you do not need to stop.