Many years ago, children in the United States were lucky if they could finish elementary school (grades1- 8). Then some children went to high school (grades 9 -12). Early in the twentieth century, some kind people said that grades 7 &8 were too old to mix with grades1 - 6, and that grade 9 was too young to mix with grades 10 -12. So the junior high school was born (grades 7 - 9). Then 30 years ago or so, some kind people said, "Let's change things again." So they came up with the current system in many American public (government-sponsored) schools: Elementary 1- 5. Middle school 6 - 8 High school 9-12

It can vary in different places in the U.S. Where I went to school.. K1-K5 was considered Elementary School K6-K8- Middle school or Junior high School K9-K12- High school