I think that your one-room school house type set-up is probably the most ideal setting for a PG kid when you don't have full-time HG/PG school options available
I've long daydreamed about a one-room schoolhouse set-up for both my kids, especially my younger, who doesn't seem to need same-age peers at his level/intensity the way DD does. He's a happy-go- lucky little dude, but his academic needs are up there. He could easily sit on second-grade reading and science classes (well...no writing), a first-grade math class, and K for writing right now, then go off to play with other four-year-olds at recess.