Here's The Naughtiest Girl: Enid Blyton

In Enid Blyton's bestselling school series Elizabeth Allen is sent away to boarding school and makes up her mind to be the naughtiest pupil there's ever been.
In book four, there's a new boy in Elizabeth's class. He's sulky and grumpy and he'll do anything to show Elizabeth up. She means to keep her temper, but it's not so easy for someone who was once the naughtiest girl in the school ...