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: When Deb is telling Nathan that she started the dealership fire they show a reconstruction in which Deb has long hair but on the 1st episode of series 3 (the fire) you see her with shorter hair same as last episode in series 2.
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.