Continuity mistake: Glen Holland owns a Chevy Corvair throughout the film. The car at the beginning of the film is a 1961 model 500 (the base model with bench seats), but at the end of the film it is a 1964 Monza (the top of the line model, with bucket seats).
Continuity mistake: Marie sits up and says "Mother, I had the most wonderful time last night." The first shot shows her fold her arms with her sheet under her arms. It cuts to a close up and suddenly more of the sheet is exposed up her belly.