Your mom and grandparents did what homeschooling parents do. In other words, you were “afterschooled”.
Where are the studies that prove classroom teaching does anything at all? Unless the informal tutoring done by parents and by paid professionals ( “afterschooling”) is measured, it is impossible to know if institutionalized teaching is in any way effective.
It is completely possible that the institutional schools are merely sending home a curriculum for the parents, tutors, and child to follow in the home.
I think we just called it being "raised." School was where I went during the day so Grandma could get the house clean, I suspect.