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.
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.