Two chemistry test plot holes.
1) I am pretty sure somebody must have brought it up, but when they traveled back four or five times for the chemistry test, what happened to the previous versions of them? Wouldn't they meet the previous group of time-traveling themselves?
2) Also another thing. The logic of the movie is, that the history repeats itself - people at the hallway do the exact same thing everytime they travel back in time. However, when they travel the first time, Quinn tells the teacher first 10 elements and the teacher asks him about the atomic weight of fluorine. The second time, Quinn does the EXACT SAME thing, he behaves the exact same way, but the teacher instead asks him to go on. WHY?! Shouldn't he ask him the same thing as previously - the atomic weight of fluorine?