in some school systems in the United States, the two or three secondary grades (7, 8, 9) of school following elementary school and preceding high school. Children served by junior high school are approximately 12 to 15 years old. The junior high school may be in a separate building or part of a junior-senior high school. In some systems, a middle school, or upper-grade centre, serves certain grades (6, 7, 8, for example) between elementary and high school.