alma mater vs prep school

alma mater

noun
  • A school, college or university from which an individual has graduated or which he or she has attended. 

  • A school's anthem or song. 

prep school

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

  • 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. 

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