Sondra Locke was offered the role of Sandy, but turned it down.
Ralph Waite played father to _Richard Thomas (I)_ in this movie, then went on to play his father again in _"The Waltons" (1971)_.
A subplot involving a wounded seagull affected Barbara Hershey sufficiently for her to change her surname to Seagull for a couple of years.
Based on a novel, the character of Dan was originally called David in the book but was changed for the movie, probably because director Frank Perry - then best known for his film David and Lisa, also about troubled teens - wanted to avoid suggestion he was making a sequel/prequel about same character.