Continuity mistake: In the beginning of the series, Haley's big family is brought up often, implying that she has 3 brothers and 3 sisters. When her mom visits her, Taylor and Quin to announce that she is dying, there is no mention of or visit from any other siblings and Lydia talks about those 3 as if they are her only children.
Continuity mistake: Firstly when they start their senior year and you see Lucas and Hayley looking at their predictions, longish hair and no beard, then it cuts to them at school and you see Lucas with a hair cut and a beard,then in the next scene, he has no beard and long hair.
Continuity mistake: Nate touches a photo on the wall of a smiling late Keith, with Lucas as a small boy. Next shot, Lucas taps on the door to let Karen know the gang is taking off, but there's no response. Next shot shows Karen sitting the other side of the door, grieving, holding that same photo of Keith and Lucas.
Continuity mistake: In this episode a sex tape shows a fling between Brooke and Nathan, and it is supposed to be from the past, but Nathan's hair is much longer and so obviously older in the video that it looks like it could have been filmed the night before, not from when he and Peyton were together.