That sounds quite ridiculous... are they then responsible for parents who get into accidents while driving their kids to school? Or is that OK because they are being delivered directly from their parent's supervision to the school's?
Do we really think that 16-17 year olds require that level of protection? We give kids that age the ability to get a drivers license. In many states you can be legally emancipated at that age - yet a school district can say you cannot choose the method you use to travel to school......
And what about after school... my parents worked. I can't remember how far back it was when I was home alone after school for at least an hour or two. What did I have to do - walk in my front door first... then I could go for a bike ride (I started doing long solo rides when I was about 14) or walk to the store or to the library? Or was the school supposedly responsible for me until I said hello to my folks? Was I violating the law for years by walking an unsanctioned path homeor stopping at a friends house!
I can understand if you ride a school provided school bus, that once you get on that bus you are then their responsibility until you get off, but in places where the school isn't providing that service IMHO it's then up to the parents and the kids what they feel is the right way to go, be it bike, walk, public bus or being dropped off.