Captain Underpants and the perilous plot of Professor Poopypants:

The fourth book in Dav Pilkey's mega-bestselling Captain Underpants series. Now with super-cool foil covers! Shiny! Fun! George and Harold aren't bad kids. They just like to "liven things up" for everybody. Unfortunately, their thoughtful jokes sometimes get them into a LOT of trouble. And when Professor Pippy P. Poopypants becomes their new science teacher...well, George and Harold almost cause the entire planet to be taken over by a maniacal, mad-scientist guy in a giant robot suit! Who will stop the perilous plot of Poopypants?!!? This looks like a job for Captain Underpants!