I know in school it may be hard to avoid one-course-per-year, but do bear in mind that if you can, it may be better to. DS10 did Algebra 1 aged 7 (in under a month, i.e. already basically knew it) but has still not learned everything in AP Calculus, not because he's slowed down in any meaningful sense, but because more mathematical maturity means it's easier to go broad and spend time on problems. Yet at various stages I have been worried about the future in a way that, so far, has proved unnecessary. So I'm firmly in the "do what's optimal this year, and worry about next year when it comes" camp.
