grammar school vs junior high school

grammar school

noun
  • Elementary school. 

  • A secondary school that stresses academic over practical or vocational education, until recent times open to those pupils who had passed the 11-plus examination. 

junior high school

noun
  • A school for children who have completed elementary school or grade school, but are not yet old enough for high school. In the US, it often includes grades 7 and 8, and possibly also 6 or 9. 

How often have the words grammar school and junior high school occurred in a corpus of books? (source: Google Ngram Viewer )