When a principal loves his school so much that he wants the children to attend classes every day of the year, it's up to his students to show him free time is a good thing, too.

The monstrous Turbo Toilet 2000 is determined to take revenge on George, Harold, and Captain Underpants.

When George and Harold hypnotize their principal into thinking that he is the superhero Captain Underpants, he leads them to the lair of the nefarious Dr. Diaper, where they must defeat his evil robot henchmen.

A skateboarding principal offers unusual incentives to his students to motivate them to learn more. Principal Klutz was hanging upside down from the school flagpole! He kissed a pig on the lips! He painted his bald head orange! And now he wants to bungee-jump off the roof of the school, dressed like Santa Claus! In fact, all the grown-ups at A.J.'s school seem to have something wrong with them. What's going on here? What are A.J. and the kids in his...