Continuity mistake: When Lily is riding her horse alongside Herman in the Dragula, the background terrain changes whether the scene is a close up of Herman or a long shot of him.
Continuity mistake: The Squire's main henchman, Denver, ends up being pushed into a fire before being stabbed to death by Sir James. When Denver is first shown falling into the fire, he goes down face-first, with his left arm catching fire. The shot changes, and then suddenly he is face-up, and it is his right arm that is on fire.
Continuity mistake: When the four kids uncouple the coach from the engine Carole is wearing trousers. The stationmaster tells them to stand clear as the engine pulls away, in the first shot of the children after the engine has gone Carole is still wearing her trousers but in the second shot Carole is now wearing a skirt.
Factual error: The uniforms worn by the engineering force are from the wrong era. Prior to 1941 the left arm rates had the head of the eagle pointing to the wearer's rear. Steve McQueen and the rest of the Engineering force rate eagle head is pointing forward, which is from WW2.
Plot hole: All the teen girls are about the same age and always in the same grade-level during their three years at St. Francis. There are no younger new students arriving each fall, nor do older ones graduate in the spring. Every student graduates at the end of the three years. Schools do not accept a new crop of students every three years.
Continuity mistake: At the beginning, Aldo escapes at precisely 3:00. But when driving away, they pass a store-front clock which reads 12:30.