I was aware my elementary school class was being split into groups by intelligence.

Starting in 1st grade, near the beginning of each year, every kid was assigned to a “group” for example: astronauts, animals and fish. It didn't take long to figure out astronauts were the excelling students, animals were the average ones and fish were the slow learners. Each group had separate workbooks and lessons. Sometimes a kid would graduate from a fish to an animal. Did any other people have this situation in school?