Goofs

George and Harold's sunglasses appear to disappear and reappear multiple times.

When small, the Turbo Toilet 2000 had a small red button on its handle. When it is enlarged, the button disappears.

When Edith is presenting her tuna casserole to Principal Krupp, the clock on the wall shows 8:05. The next time the clock is seen it shows 10:05, then back to 8:05 when the scene ends.

In his very first lesson Prof. Poopypants spins the globe on the teacher's desk. When the globe stops spinning, the students see the part of Europe. In the next moment it's Asia, although nobody touched the globe.

When George and Harold tried to leave Mr. Krupp's office, he pushed a button to lock the door. But in the previous shot, the button wasn't on his desk. In the same scene, the recycling bin disappeared, reappeared, and was far away from the outlet.

Professor P's resume is originally in a red folder and the next time we see it it's in a manila folder. But, it's very likely that they put Professor P's resume in a new folder when he was hired.

The name of the school changes back and forth from Serome Norwitz to Jerome Horwitz and the flyer that is advertising for the school says, Jerome Horowitz. However, due to George and Harold being pranksters, it is possible that they changed the school's name for their amusement.

When Captain Underpants jumps out the window, the glass appears to be broken & jagged; but once he's outside, the hole in the glass is the exact shape of Captain Underpants. However, this is merely an illusion since indoors the hole is seen in close-up so is less recognizable, but actually it's still the same shape. For instance, the jagged edges next to George are really the Captain's left armpit with the arm curving round, below which is a sharp angle made by the Captain's raised left heel with the left flank of his torso; then next to Harold is the crease between the Captain's right buttock & right leg, with his right armpit just visible up by the boy's head.

When Harold and George are taking Principal Krupp home, they use his license to find his address. His ID shows the zip code for Piqua, OH as being 45355. Piqua's zip code is 45356. 45355 is actually Essen, Germany's zip code.

Every time George and Harold snap their fingers, Mr. Krupp turns into Captain Underpants, and takes off his clothes. But when Captain Underpants was pretending to be Mr. Krupp, he didn't take off his clothes when George and Harold snapped their fingers to keep him from turning back into Mr. Krupp.