Your options depend on where you live. G&T program might be the most straightforward solution, but not all school districts have these. My son did G&T starting in 5th grade, but then we hired a college student to tutor him once he got beyond the level of math they covered in G&T. He had run through all of H.S. math by the time he was H.S. freshman, but fortunately we lived in a very enlightened public school system which let him start taking college-level courses in a local public university while he still was in H.S. It was a hassle logistically, and we sometimes ended up relying on college student drivers, but well worth it.
Because we were grateful to get the special permissions needed for him to come and go from H.S. on a non-traditional schedule, we never pushed on the issue of whether the school system should be defraying any of these costs we incurred: had he been developmentally impaired, the cost to “mainstream” him presumably would have been much greater and I further presume the school district would have been legally required to foot the bill. But my general impression is that most school districts feel far less obligation to meet the needs of G&T students. Good luck.
We had this as well. My son could have gone to the participating uni for some additional math, but the travel hassle and iffy neighborhood of the uni made it a no go. He still got into Michigan, which was all we wanted (well ok, I wanted him to refuse Harvard after it invited him to apply, but he would have gone to Michigan anyway). : )
“But my general impression is that most school districts feel far less obligation to meet the needs of G&T students. Good luck.”
There are federal and state laws saying that schools must properly serve “special needs” kids, but gifted children are not covered by the Federal law or most of the state laws. Gifted kids can often be helped by skipping a grade, which saves the school district (and the taxpayer) money, but schools officials want to maximize enrollment.