I see the argument you are making and just want to suggest that this law is trying to help out the kids who are both capable of getting to school on their own regardless of start time, who would also benefit from the extra sleep. I suspect that this is the majority of the population of teenagers. Public schools are not really a free market where kids get to pick and choose based on features like start times. Most are selected because it is the only practical option for the family's means. In the absence of market pressure, using legislation to improve people's lives isn't wrong.