elementary school vs prep school

elementary school

noun
  • A school for children, typically older than toddlers and younger than adolescents. In the U.S., elementary schools cover grades 1 through 5, and the ages of the children are usually 6-11 years. At a minimum, elementary schools will teach basic reading, writing, arithmetic, and history. Historically also used in the UK. 

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 elementary school and prep school occurred in a corpus of books? (source: Google Ngram Viewer )