R.L. Stine 
Rotten School #10: The Rottenest Angel [EPUB ebook] 

Angel Goodeboy is a perfect angel . . . You can almost picture a halo over his head! He even wears a T-shirt that says "Mommy’s Little Angel."Bernie Bridges is horrified when Mrs. Heinie makes him share his room with Angel. She wants Angel’s goodness to rub off on Bernie. But wait a minutewhen no teachers are watching, Angel is no angel!The little sneak takes over Bernie’s room. He steals away Bernie’s friends. He charms Bernie’s girlfriend. Everyone loves Angeleven Bernie’s pets! There’s only one way for Bernie to rule the school again. He’s got to get rid of this kid! But how do you get rid of an angel?