My son was in the same situation: 8, in 4th, doing 6th grade math. He was in a small school, and there was another student in 5th who was ready for 6th grade math, so a teacher taught both of them.
My question is, why do they have to provide transportation if the middle school is only a block away? Can't he just walk or ride his bike? Is there a highway in between, or would he just walk down the street to the school?
If they can't let him go alone, there must be someone who can spend 10 minutes getting him there and someone else who can get him back. Doesn't sound like it should be a big deal to me.
Is there a community college or university where you live? If your son ages out of the school's math curriculum, he could take statistics or extra calculus or whatever. I live in California, too, and high school students can take community college courses for free here.
I'm also not sure why the school thinks he wouldn't have the correct number of math classes for college. He'll have taken them --- it's just that he'll have taken them in 7th grade rather than 10th!
Val