If not through GT stuff at the school or AP classes, where is one to find the like souls in a big high school, then?
In my "big" high school, the HG+ kids were generally found hanging out at lunch and before and after school either in the music room, the science research and comp sci teachers' rooms, or the library, or at the science fiction book club meetings...but this was at least as much because those places happened to have the few highly gifted adults in the school running them as it was because the gifted kids naturally gravitated to those subjects.