Audio problem: In the scene where Freddy cuts off a doll's head to replace Wondermut's old toy Bob, there is a close-up of the doll head being shaken with Freddy's head visible in the background. You hear Freddy saying, "Look Wondermut. I found Bob," but you can see that Freddie's lips aren't moving.
Continuity mistake: At the end of the movie, when the kids are taking the test, the girl that is pregnant breaks her pencil in half because she is having contractions, but in the next consecutive shot (no time has passed) her pencil is intact.
Continuity mistake: At the end when Shoop is kissing Robin on the beach, we see Bob's head wash up on the shore. Wondermutt runs behind the couple to get the toy head behind them, yet, in the next shot Wondermutt picks up the toy head which is now in front of them. Note the tide.
Revealing mistake: When Shoop first meets his students, he asks the pregnant girl why her grades went from A's to C's, and she stands up to reveal that she's pregnant. When she does, she pats her tummy once and it makes a loud, hollow sound like someone smacking a basketball.
Continuity mistake: When Gills is trying to find someone to teach the summer Remedial English class, Shoop decides to hide behind the bush in the parking lot to avoid being asked (he's going to Hawaii with Kim). Gills finds Shoop when Wondermutt (the dog) follows Shoop behind the bush. But, if you look closely, you'll notice that there's a shot of Wondermutt following Shoop behind the bush and then two shots later he runs behind the bush again (that's how Gills finds Shoop). Wondermutt runs behind the bush twice.