grammar school vs middle 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. 

middle school

noun
  • A school which crosses the traditional divide between primary school and secondary school. 

  • An educational level or stage between primary school and secondary school. 

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