Body Switchers from Outer Space — Nina Kiriki Hoffman

COME BACK WITH MY BODY!
Will "the Spill" is a total klutz. He'd give anything to be Chad -- the most popular kid in school -- just for one day. Chad never trips, or falls, or drops anything.

Then Will gets his wish. Chad says he's got a body-switching machine. And he wants to switch bodies with Will!

Will decides to do it. And it works! He loves being Chad -- until he finds out Chad's horrible secret. And realizes he's trapped in Chad's body forever!