Ivy and Bean and the Ghost That Had to Go by Annie Barrows
Now that Ivy and Bean are friends, they do gymnastics club together, sit together in Ms. Aruba-Tate's second grade, and tell each other their darkest secrets. And when Ivy discovers a ghost in the school bathroom, it will take both girls' courage and imagination to make it go away. Another entertaining installment in this series about two mischievous, funny, clever girls.