Continuity mistake: Kelly said her youngest brother can burp his whole name Kenneth Leonard Kapowski in one burp. However in the previous year, Kelly had an infant brother named Billy. According to this info, unlikely Kenneth would be younger than Billy.
Continuity mistake: In this episode, Screech's mother kisses her Elvis statue before her trip while it is facing towards the right; indicating that this is the correct way that is should be facing. However, when she comes home after her trip the "new" statue is facing the same direction; right. She complains and says that the statue should always face towards the kitchen so he can see her cook; which is towards the left.
Continuity mistake: When Zack is in middle school, his teacher, Miss Bliss wants to talk to his father. At that time his father's name is Peter Morris and he is an older man and unmarried. When Zack is in high school and Mr. Belding wants to talk to him about the ski trip, his name is Derrik Morris and he has a mother.
Continuity mistake: In the scene where Max has Zack bring Kelly a Coke, you can see the glass only has one straw in it. You can verify that it's simply not two straws stuck together when he lays it on Kelly's table. As he lays it down, the straw swoops around the outer perimeter of the glass and it can be verified that it's only one straw. However, when Kelly decides to take a drink of it there are now two straws in the glass.
Continuity mistake: During 8th grade in one episode, Zack talks to Ms. Bliss about having had to use his sister's bike for a project. In high school, many episodes have Zack being an only child (further proven several times when Derrick Morris would tell Zack that "he and his mother were more important than his job").
Continuity mistake: When the teacher is going through the study fast, you see Kelly stretch her wrist as it hurts from writing so fast. While she is stretching, behind her you see Zack putting on his headphones. A few seconds later the camera is on him and he is putting the headphones on again.
Continuity mistake: At the end when they finish the commercial, nothing at all is the same on the playback as what they showed them do. None was the same. The wording and also the places and stances everyone was doing. The entire thing was different in the playback.