Audio problem: When singing Reproduction, a boy sings "Oh I think I'm gonna throw up"; yet he sticks his finger down his throat and keeps it there until the line is over, never closing his mouth; how did he make the 'p' sound on 'up' without closing his lips together? The words are pronounced very clearly and the camera doesn't cut from his face until after the line is done.
Continuity mistake: When Michael is doing his bike up and is spraying the cycle's gas tank, his hands are full of oil, but in between his fingers are clean. This shows that is is obvious someone has smeared the oil on, otherwise in between his fingers would be just as dirty. And his hands wouldn't be perfectly black, they would be streaked.
Other mistake: Eugene is suspended above the stage with the box of paper leaves and snowflakes ready to throw them down at the correct moments; but when the Fall section of Girl For All Seasons is on he doesn't throw any leaves. Also, the amount of snow coming down over the stage at the Winter section is completely disproportionate to how widely and evenly Eugene could distribute it.
Plot hole: Nogerelli says to himself that the gap past Deadman's Curve must be 100 feet wide. How on earth was Michael meant to have made a jump of 100 feet (or even a few feet less) after both being slowed down by crashing through the wooden barriers and also by not having a ramp and therefore no upwards boost? He would have plummeted to the bottom.
Continuity mistake: In the scene at the end when Johnny gets out of the raft, you see him walking up through the back of the crowd and in the next shot, he is throwing his costume off his back on the side of the pool, then cuts back to him coming between Michael and Stephanie.
Factual error: When the substitute teacher is teaching the children about reproduction, the Playboy magazine is from September 1962, but the year is supposed to be 1961.
Continuity mistake: The scene when Michael is jumping over the cop car and it cuts to a front shot of the jump, you can see Stephanie, Paulette and Rhonda watching him jump in the background, even though Rhonda had walked back inside the bowling alley with Goose and Davy before Michael reappeared from the chase.
Other mistake: When Michael is sitting down singing the song "Charades," there is a window behind him. Dolores comes up to the window and waves for the Pink Ladies to come outside. First you see Paulette go by, then Sharon, and the third girl is obviously supposed to be Rhonda, as she is wearing a Pink Lady jacket. If you look at "Rhonda's" face, you can see it is not Alison Price, who portrays Rhonda throughout the rest of the movie. (01:22:00)
Other mistake: The movie starts in September 1961 and we are told that the talent show is in June. During the talent show there's a big banner saying 1961 when it should read 1962.