There's an Alien in My Backpack(2000)
(The ninth book in the I Was A 6th Grade Alien series)
A novel by Bruce Coville
Pleskit has always siad that he's not necessarily the first alien kid to go to school on Earth. He's just the only one who's doing it openly.
Tim discovers the truth of those words when he meets a two-foot-tall alien, Beebo, who is stranded here and wants desperately to get back to his own planet. Unfortunately, Beebo's presence on Earth could cause a diplomatic disaster. So Pleskit can't ask his Fatherly One for help.
And help is what the boys need, because Beebo is an imp! He's hooked on mischief, and can't resist using his powers to cause chaos in the classroom and havoc on the homefront.
Pleskit and Tim have faced plenty of alien menaces. But can they survive an incredibly cute prankster who as a genuine gift for causing the most embarrassing trouble ever?
Used availability for Bruce Coville's There's an Alien in My Backpack
January 2000 : USA Paperback
December 2000 : USA Paperback