And... he's off to fourth grade math! I give the school a lot of credit for handling this on their own. They had the GATE person give him the end-of-year 3rd grade math assessment, which he completed in 30 minutes (I got the impression that was unexpected). He missed some questions but scored solidly enough that they decided he had mastered the 3rd grade material and that they were not providing adequate instruction by having him in 3rd grade math. So he has also now taken the 4th grade end-of-year math test, only scored about 40% on it so they are going to try the 4th grade class for math next week.
The teacher has already called me and explained where they are at, their online resources and so on. Schedulewise, it's a bit less smooth due to the time of math for that grade, but the two teachers are working out a plan. Wow.