My grand niece (age 8) is said to be a budding supergenius. She is going to some special class for 'gifted children'. Well, I'm waiting to see anything at all that might be different. However, my mother has a genius IQ, so maybe it skips around from generation to generation.
Throughout history, the most obvious sign of a genius is that his teachers hated him. The academic system is the outgrowth of a cult called Akademos in Greece. It was a grove sacred to the goddess of wisdom. Membership was by invitation only. They claimed ownership of all knowledge and discoveries by outsiders were rejected. Aristotle was the most famous member, and two thousand years later his name is still a synonym for "arrogant jerk".
So what happens to a little genius? In first grade the teacher tells him "Don't get ahead of the class," as if it were his responsibility to remain stupid until he has completed the required classes to be smart. The same applies at every level but gets more insulting at the higher levels, until most of your geniuses just get ground down. And then society rejects them as "morons". Either that or they reject society and go live in a forest somewhere.