Continuity mistake: When Ren and Ariel join Willard and Rusty in fighting Chuck and his friends, Chuck says to Ren "Why don't you come down here." As he says this he makes a "Come over here" gesture with his hand. The shot is from behind him, but then when it switches in front of him his hand is already down by his side before he put it down in the previous shot.
Continuity mistake: Ren leaves the High School to let off steam after his fight with the principal. He backs out of the parking space and the car has no hood on the engine. In the next shot, when he drives into the warehouse to do the dance number, the car has a hood on the engine.
Continuity mistake: When the main characters are dancing at the drive in, Ren makes his way over to Ariel and dances while she is leaning on a car hood. When he gets to her the shot shows what's behind him (slightly at an angle) we see Chuck sitting up on his truck bed. When the shot changes to show his reaction he is leaning back, then sits up.