Reading the back of the book won't do. In fact, at first I didn't want to read the book. But because all Louis Sachar's books are good, I read it and it's GREAT!
When Scott becomes friends with Roger and Randy and the three plan to steal Mrs.Bayfield's cane, Scott invites his friend David to come along. And when they get there, Scott grabs the cane, Roger and Randy pull pranks, and David shows his middle finger.
A lot of good for David! She puts a curse on him. He comes into Spanish with his zipper down, breaks a tube in Science, becomes friends with Larry and Mo and the three become the Stooges: Larry, Mo, and Curly.
To find out what else happens to David and his curse, read THE BOY WHO LOST HIS FACE. (It's at your local bookstore.)