Continuity mistake: In the classroom after Cindy is done explaining her dinosaur report she heads back to her desk, Jimmy and Cindy get in an argument when it cuts to Jimmy, in the background you see Carl standing up and not sitting.
Factual error: When Cindy is giving her "fossil-to-chromosome ratio" report, she calls her model dinosaur skeleton a plesiosaur. However, the skeleton is of a bipedal dinosaur (likely a hadrosaur, judging by the "duckbill"), while plesiosaurs were aquatic reptiles with flippers instead of feet.
Plot hole: When Jimmy is in his little rocketship launching his toaster satellite into space, the morning newspaper that his dad is reading already has the photo of the rocketship on the front page as a UFO. But the military jets were the first ones to spot the rocketship, the newspaper couldn't have gotten the story and printed it out that quick.