Revealing mistake: When Dennis gets frustrated with the contraceptive foam and throws it aside, it is obvious that a machine is at the bottom of the screen to make all the foam squirt out, since it sprays from a different location than from where the cannister was thrown.
Continuity mistake: Verena's cigarettes change place when she exchanges them from Tomas.
Other mistake: Towards the end of the film, when the girls have locked themselves in the school, and Odette addresses the girls about voting what they feel, Tinka and Tweety hand out the ballots. When Odette says "You think times have changed, and we go our own way...", we see the camera focus on a group of girls. Now if you look closely at the middle row, at the girl on the right, you won't be wrong if you think that that's Kirsten Dunst. What's wrong with her being in the picture? Well, by this time in the movie, Kirsten Dunst has been expelled from the school and shouldn't be in that frame. We know this, and it is confirmed that she wasn't still at school by her appearance at the end of the film, when she arrives with Frosty in his car and says "We drove down as soon as we heard the news on the radio!" (01:27:00)