Ned's Declassified School Survival Guide - Mixed-Up Days
In the episode "teachers", watch when Ned starts kissing up to the science teacher in order to get a good grade. He says "i'm really looking forward to todays quiz." This happened on Tuesday. You can tell by the calender scenes in between.
After, on Thursday, Ned is dressed up in a science suit and says "yesterdays quiz was great". (something like that). Anyway, he says this on a 'Thursday'. He says 'yesterdays' quiz which would have been a Wednesday. He says that the quiz was on Tuesday.