playground vs schoolyard

playground

noun
  • A large open space for children to play on, usually having dedicated play equipment (such as swings and slides). 

  • Any physical or metaphysical space in which a person or organization has free rein to do as they please. 

schoolyard

noun
  • An open field near a school used for recreation by the students. 

  • The grounds around a school. 

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