Trouble with Buster

This is the first book I remember reading, and it was my favorite book when I was four. It's at about a second grade reading level, about a girl named Bernice and the trouble with her friend Buster, told by her older brother. When Bernice starts school, she promptly finds herself in trouble for various things. Everything, she claims, was Buster's idea. Her brother tries to help her find ways to stay out of trouble, and help her adjust to school, but nothing seems to work. Then he finds out something that might just solve the problem...