Continuity mistake: In the scene at the cove where Suzy and Sam are talking after swimming, the flower stem over Sam's ear keeps changing positions. In some shots it's parallel to the temple on his eyeglasses, and in others it's drooping down over his cheek.
Continuity mistake: In the scene where Scoutmaster Ward wakes up to an empty Camp Ivanhoe, he is without his neckerchief at the ironing board; then he walks through the deserted camp and the neckerchief is on. In the next scene, as he is ringing the bell, the neckerchief is gone again.
The VW Bug that the belfry falls on is a later model than 1965 when the movie is set. The larger tail light with yellow on the lens seen on the VW in the movie didn't come along until 1968. The one in the movie may even be of early 70's vintage.