When Valerie and Chas arrive at the caveman party, the saber-tooth teeth on Valerie's necklace are all pointing outward as normal. In her closeup when she says "Jason said it would be great", the teeth on her left are pointed inward toward her chest. They then return to facing out in the next shot.
During the final dive meet the diver who gets blinded by the mirror courtesy of Derrick has his appearance change from skinny with longer dark hair before the dive to a much stockier individual with short blonde hair during the dive.
At the final dive meet Coach Turnbull is wearing a striped knit tie, while he is at the judges table explaining that Thornton is an eligible member of the dive team, the stripes on the knot of his tie change.
When the football team confronts Derek, Jason is standing more towards Lou near the booth. When the football player picks up Derek, Jason is now behind Derek. In the next shot when Thorton steps in, Jason is back near Lou.
When Prof. Terguson is talking to Melon, the student sitting behind Melon is wiping his forehead with a handkerchief. While he is doing this the camera angle changes and the student is seen with a notebook open on his lap that he is looking down at and the handkerchief has disappeared.
When Chas and Valerie first show up at the caveman party, a girl in a pink outfit passes them and leaves the room. The scene then goes to a wide shot of the party, and the girl in pink is sitting on the couch. When it cuts back to Chas and Valerie, they walk into the room and past the couch, where there is no sign of the girl in pink.
When the party ends and Thornton is swimming a boom mic operator is visible. After he dives in the camera cuts out and you clearly see a boom mic operator in the window behind the pool. He's wearing a red shirt and clearly holding something.
During the final scene, Thornton Melon gives a speech as a freshman for the graduating seniors. Even though he never attended college before, he is wearing not only graduation robes, but doctoral robes. As part of his generous donation, however, he may have been bestowed an honorary degree.
In several scene it is indicated that it's cold outside by wearing jackets. But however during the pool scene everybody is outside without shirts on or dresses in bikini. Also people are swimming in the pool like a regular summer day.