Continuity mistake: When Shawn is loading up his backpack with food from the catering table, a production assistant emerges from the kitchen and asks him if he's part of the interview. After Shawn says he is, the assistant walks away towards the front door. When the shot changes to the couch where the family is being interviewed, the assistant is nowhere to be seen, even though he walked right into the area of the shot. When the shot changes yet again, the assistant is back by the catering table, standing with his arms folded.
The Last Temptation of Cory - S3-E9
Deliberate mistake: When Cory calls Topanga from Missy's phone, he starts having a conversation with her as soon as he finishes dialing her number, with no time for the lines to connect.
Continuity mistake: In this episode Cory has a full length locker, but in the previous episode (Hometown Hero) He has the top locker. It's always in the same stop, so there is no way that he changed lockers.
Other mistake: When Eric asks Mr. Williams why everyone is applauding Frankie missing a shot in their game of pool, Mr. Williams notes it's because no-one has ever seen two people play for three hours without sinking a shot. However, if you rewatch a couple of times the part where Frankie takes his shot and you count the balls on the table, there are only 14, not including the cue ball, when there should be fifteen. If by chance a ball was knocked off the table, then given how much the crowd was into the game, someone would have told them they needed to place the ball back on the table.
The Pink Flamingo Kid - S3-E17
Other mistake: When Eddie busts Cory filming him and his cronies, he spends a few moments intimidating Cory before snatching the camera out of his hands and throwing it against the ground. After Shawn breaks up the situation and notes that they broke the camera, Cory remarks that they didn't get the tape and proceeds to pull a tape from under his jacket. Cory's hands are both visible gripping the camera the entire time that Eddie is confronting him, and he didn't have the opportunity to retrieve the tape when Shawn intervened, so he couldn't have had the tape tucked away.
Deliberate mistake: When Alan is trying to rush Amy out of the door, she yells from upstairs that she's still shaving her legs. A mere 20 seconds later, she comes downstairs wearing a dress and nylons. Even if she was for some reason shaving her legs while wearing a cocktail dress, that still wouldn't be enough time for her to clean off her legs, put nylons on and then walk downstairs.
The Last Temptation of Cory - S3-E9
Continuity mistake: When Shawn walks out of the front door of the Matthews' house, you can see some diamond fencing with vines on it on top of a brick foundation. But establishing shots of the house show no such feature by the front door.
Chosen answer: In the present day, with the United States abiding by more stricter school health laws, for the most part this wouldn't be in school cafeterias as many cannot even have carbonated beverage machines now. However, in the 90s when the show takes place, it wasn't unheard of for there to be coffee machines in the cafeteria of small schools where the teachers eat with the students as we see them do often in the show. The idea being that the cafeteria was small enough so a teacher or hall monitor could catch a student before they could drink the coffee.