At the 36 min mark, Caroline's hair is mussed from a previous take of putting her bonnet off and on.
The teacher Eliza Jane Wilder disciplines Bartholomew by telling him to stand in the corner. Schools during the 1870s still used corporal punishment for discipline as the modern day method of time-outs didn't come to use until the 1950s.
At the first confrontation with Mr. Slater the fence behind him is 1970s mass produced.
The Ingalls children try to fool Bartholomew by having him think a papier-mache boulder was real and that Albert was a werewolf that could hurt him. Even if Carrie hadn't ruined their plan, Bartholomew would have known the truth when Albert brought the boulder to class and there would be nothing to stop him from going back to his bullying ways.