Just between us — Susan Beth Pfeffer

An incurable gossip tries to learn how to keep secrets to herself

Sometimes Cass just can't help herself. Tell her something personal, even something embarrassing, and before you know it, the whole school will have heard. It's not that Cass doesn't want to keep secrets -- she just doesn't know how. After her bad habit lands her in a fight with one of her friends, Cass asks her family for help. Mom proposes a psychological experiment. Every time Cass manages to keep a secret, she'll get a dollar -- and a lesson worth far more than that.
 
It's easy at first, but pretty soon Cass is so full of gossip, she feels like she's going to burst. When an earth-shattering secret traps her in the middle of her two best friends, she learns that sometimes it's more important not to keep your mouth shut.