comprehensive school vs prep school

comprehensive school

noun
  • a normal secondary school, accepting pupils of all abilities; replaced the secondary modern schools and grammar schools 

prep school

noun
  • A private primary school which prepares its pupils for the common entrance examination most commonly at the age of thirteen, and subsequent entry into public school. 

  • A private or public school intended to prepare its students to get into prestigious universities. 

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