The scene where the boys all suddenly start singing "Hitler has only got one ball" was unscripted. Director Larry Peerce continued filming to see how it played out, with the scene ending up in the final cut.
John Knowles, author of the novel, "A Separate Peace" on which the movie was based, attended Phillips Exeter Academy where the movie was filmed.
John Heyl had little interest in acting and went on to become a high school teacher in Flagstaff, Arizona.
With the exception of Parker Stevenson, most of the boys featured in the movie were real students at Phillips Exeter Academy where the movie was filmed. This includes John Heyl who played Finny. Heyl's Father was the school's on-site doctor.