Well, the money saved on buses is actually quite simple (but flawed): they won’t be driving in Rush Hour Traffic. Therefore, they can use less gas (and possibly fewer busses will be needed over all, depending on if they had to run buses as below capacity just to make up for traffic delays). Of course, Rush Hour truly starts around 3:45/4, so instead of spending money on gas in the morning, they'll be spending it in the afternoon (but they still might be able to use fewer buses, because the school cares about when time you get and leave from school, not when you actually get home).
Starting school around 9:30 actually makes a lot of sense; teenagers aren't really morning people, on average. Waiting until closer to 10 makes it more likely that students will profit from those first classes.
So students will have less time to work at a job. It sucks for those who, for one reason or another, need the money, but society's concern with teenagers shouldn't be about their economic contributions but about their education. It would actually be desirable if fewer teenagers wasted their energy on "jobs." Unfortunately, as mentioned, this screws people who actually need the money.
In all likelihood, practice for sports would be moved to before school (or possibly split before and after), but sports are also not really the concern that society should have for teenagers. Sure, they teach valuable "life lessons," but so does band, theater, most clubs, etc. Loosing sports won’t be the end of the world.
As for crime, etc., in all likelihood it will decrease (come on, when do teenagers get up before they have to?), as they'll have less time in the afternoons and more time in the mornings (which will probably be devoted to sleep). At the worst, it will just switch the times when such dubious behaviors occur, from the afternoon to the morning.
But if you want an education, school is really not the best place to find it. You said you'd have loads of homework from advanced classes. If those advanced classes were actually good, you wouldn't be assigned "loads" of homework (as the majority of homework assigned isn't actually useful).
You are better off getting that High school Diploma, just because people expect you to, but look to yourself for your actual education. Read books that interest you, engage in debates (like here on the compendium, other websites, etc), read newspaper articles, research, undertake “projects” just for the fun of it, etc. What you learn of your own volition will probably serve you better than what you learn in most classrooms.
