The eagle on top of the clock disappears and reappears between shots.
When London 'stamps' Ivona's paw with ink, there is no ink on her paw.
In the scene where they are having the finals, the things on the desk change a few times.
The whole episode is based on false facts. Cody was getting an A in woodwork and Zack was failing in all his classes the previous year at school (according to their report cards in Ep "Smarter and Smarter"). So Cody knows a lot more about woodwork than Zack and should be able to make a clock, never mind a birdhouse, and Zack should not be able to make a clock.
While London is reading her story with the group of children, the little girl in the far left recites London's lines.