Other mistake: The "roach" Tim and Francis were to share with the magazine stand man had a length about equal to the width of the man's index finger. The man was able to hold it and take a drag without burning his fingers, but it would have been impossible for Tim and/or Francis to do the same - yet they managed to "get high."
Factual error: Sister Assumpta takes the book from the boys and puts it in a drawer of contraband in her desk. There is a shot of the inside of the drawer and you can see a Marvel GI Joe comic book. This film is set in the late 1970s, but the first issue of GI Joe was released in 1982.
Continuity mistake: In the animated sequence, just before the kids destroy Sister Assumpta's office, Skeleton Boy's cast remnants switches from left arm to right arm and back to left arm. The left arm is the correct side as Tim (who is Skeleton Boy) had his cast on his left arm. (01:20:00)