The Only Girl in School by Natalie Standiford

She's the only one who knows what it's like to be the only one.When Claire's best friend, Bess, moves away, she becomes the only girl left in her entire school. At first, she thinks she'll be able to deal with this -- after all, the girls' bathroom is now completely hers, so she can turn it into her own private headquarters and draw on the walls. When it comes to soccer games or sailing races, she can face off against any boy. The problem is that her other best friend, Henry, has begun to ignore her. And Webby, a super-annoying bully, won't leave her alone. And Yucky Gilbert, the boy who has a crush on her, also won't leave her alone.It's never easy being the only one -- and over the course of a wacky school year, Claire is going to have to make it through challenges big and small. The boys may think they rule the school, but when it comes to thinking on your feet, Claire's got them outnumbered.