Creature Teacher: The Final Exam (Goosebumps: Most Wanted #6) by R.L. Stine

It doesn't take long for Tommy to find out he's in big trouble. His whole family is obsessed with "being the best" and so he is sent off to a special camp to help make him into a "winner." When Tommy gets there he sees that something isn't right. All the kids are so competitive - it's almost like their lives depend on it. There's talk all over the place of a special "teacher," Mrs. Maaargh, who takes her lessons on winning very seriously. Can Tommy survive The Final Exam?