Everything in Its Right Place - S4-E11
Character mistake: Lucas is seen placing flowers on Keith's tombstone, which states he died on January 23, 2006. In the next shot Lucas places a single flower on the grave of Jimmy Edwards, who died the same day and in the same scene as Keith, yet his tombstone states that he died on March 1, 2006.
Character mistake: When Mikey looks at the Picture Day schedule, he points out that 4th grade is going last. However, the schedule says they are after 3rd grade and before 5th grade, actually making them fifth. The faculty is actually listed last on the schedule.
No Victory in Semi Final - S1-E21
Character mistake: To signal the end of the match, the referee blows the whistle just once instead of three times. (00:10:25)
The Purple Panther: Part 1 - S3-E6
Character mistake: In the song 'The World Goes Round', Stingy sings about dinosaur bones from the Stone Age (the second verse). The dinosaurs were wiped out about 65 million years ago while the Stone Age started 2.5 million years ago, an obvious time gap.