When I was in elementary school, the school system went like this.
Elementary:K-6
Middle School:7-8
High School:9-12
But then a couple years ago, they changed it to this:
Early Learning School: Prek-k (PreK is optional here, you're allowed to another school, and then come back for Kindergarten.) (1 school)
Lower Elementary:1-4 (3 schools)
Upper Elementary:5-6 (2 schools)
Middle School:7-8 (1 school)
High School: 9-12 (1 school)
They changed it when I was going into 5th grade, so I only had to change once before going to Middle School. Imagine the kids who were/are starting kindergarten? They would have to go to 5 different schools before graduating High school!