Each state or even district divides it differently. Where I am, 11 year olds would either be in 5th grade (primary/grade school) or 6th grade (middle school). But sometimes 5th is lumped in with middle school. Sometimes they have junior high which is something like 12-14. They usually consider high school (14/15-17/18 year olds) to be secondary school. This goes back to my grandpa's time. Most people in his generation got 8th grade diplomas for finishing primary school. Secondary school was high school, but wasn't mandatory or even that common in many places.