During the math lesson in the beginning of the movie, the teacher has her students chant that common denominators are important; but the exercises on the board are on division of fraction, not addition or subtraction, and that has nothing to do with finding common denominators. A few moments later the same teacher praises Gilly for knowing "divisional fraction", which is another nonsense, as there's no such term - it'd division of fractions that they were doing in class.
This movie is set in Maryland during the Thanksgiving & Christmas holidays, yet all of the trees and lawns are in full summer splendor.