Welcome, Padrickk,
In addition to the suggestions above, your DC might enjoy some of the materials from Art of Problem Solving--which was originally a coaching resource for IMO-type students. They have full-course textbooks (digital and paper) and live courses with appeal and rigor for deep mathematical thinkers, as well as books focused on competition-type problems. Because the approach is quite different (far more conceptual) from many standard texts, even repeating algebra I (called introduction to algebra A) can be a valuable learning experience. The courses are accredited by WASC; some districts may accept them as transcript credit, or at least as leverage for placement to higher-level math at high school entry.
And FWIW, my upper school DC is in AP math class with classmates two years older, and does not appear to be having social concerns. But this is, of course, highly dependent on the exact child in question.
