junior high school

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A school in the US system generally including the seventh, eighth, and sometimes ninth grades.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun education A school for children that have completed elementary school or grade school, but are not yet old enough for high school. In the US, it often includes grades 6 or 7 through 9.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a secondary school usually including 7th and 8th grades