Clarifying my previous post
I'm not sure if dual enrollment would be the right term for what we'd be looking for. By the time our son finishes calculus he'll have enough high school math credits (even though he wouldn't be in high school yet).

So he'd be needing university maths courses to keep moving in maths (while doing needed high school courses in other subjects), but he'd only need university credit (not high school credit) for maths.

So it would really be a case of taking some university courses totally independently of the K-12 school. I know there are other options like AoPS for some courses, but university is the logical choice for courses that will have to be taken eventually anyway.

Anyone have experience with this?

Also CFK, what does it entail to "graduate" from homeschool?