When Boots is being an obnoxious roommate to George, he plays a full drum set right behind him. There is no way Boots could have brought in, never mind set up, a drum set right behind George without being noticed until he started playing.
When Chris Talbot paints a wall like a realistic hallway that Cathy runs into, a la Roadrunner cartoons, there are two issues. Firstly, as a non-existent hallway, it wouldn't be on anyone's route to get anywhere. Secondly, it looks accurate to the camera, a 2-dimensional image that mimics a 3-dimensional one only has that effect from one angle. If it looks right to the camera, it would be an obvious fake from Cathy's angle.
When Scrimmage's moves in, Sturgeon says Bruno & Boots' old room has been turned into a therapy room for Scrimmage. With such a large influx of students needing bedrooms, Mr. Sturgeon wouldn't make such a foolish choice as to allow a dorm room to be used as anything but a dorm room.
When Mr. Sturgeon talks about how they'll eventually leave Macdonald Hall, Bruno Walton tries to tell him he has a plan for that, Mr. Sturgeon interrupts, calling him "O'Neal" instead of Walton, then moments later correctly calls Boots "O'Neal". Mr. Sturgeon is well above average as a headmaster, he would never make that mistake.
When Bruno, Boots, Cathy and Diane confess to Sturgeon and Scrimmage that the prank war was merely an attempt to split up the schools, that ends this tactic, yet neither Bruno nor Cathy trust that the prank war is over.
When Mr. Sturgeon and Miss Scrimmage are discussing the dance they have just planned, Sturgeon expresses his disagreement by saying "Forced gatherings meant to create enmity usually do the exact opposite". "Enmity" means to be actively opposed to, hostile. He meant to say - and the closed captions show - "amity", which means friendship, peaceful harmony, understanding (the actual goal of this dance). The "nm" sound is unmistakable. Sturgeon is a highly intelligent headmaster of a school, above all others he wouldn't make such a mix-up.