I would ask parents of other math accelerated kids. As mentioned by others, many schools with staggered start times (HS starts earliest, elementary is last to begin the day) will have a first period math class. Kid gets on the MS bus in the morning, takes math first period, then is bussed to elementary when they are just starting their day.
Depending upon where you live, this could get trickier in HS. If there are colleges nearby, accelerated HS kids can just take a class at a college. Folks in this district are fortunate to have three 4 year colleges within a mile of the HS. My kids will not need to use this resource, but they know kids that started college courses in 8th or 9th grade. HS math goes through Linear Algebra though, so HS courses are adequate for most kids.
