Continuity mistake: When Freddy is talking to Eddie about going to play pool, his knapsack strap goes from hanging off his shoulder in one shot to being on his shoulder in the next.
Factual error: In one scene Fred Tate is explaining to his mom, Dede, what a 'lepton' is. He says first "A lepton is a Z-particle", then furthermore says "Do you know what protons and electrons are? [...] Well leptons are even smaller." In fact, electrons *are* a kind of lepton. Also, there is only one Z-particle, and it is quite different from leptons.
Fred Tate: My first grade teacher, Miss Nimvel, told Dede that I never paid attention. That I was probably retarded, and that I had a very limited future as a citizen of the United States. Then a week later, she said I should probably skip second grade, maybe even skip elementary school altogether.