Haunted School by R,L Stine
He's hearing voices ...from another world. Tommy Frazer's dad just got married. Now Tommy's got a new mom. And he's going to a new school - Bell Valley Middle School. Tommy doesn't hate school. But it's hard making friends. And his new school is so big, it's easy to get lost. Which is exactly what happens. Tommy gets lost - lost in a maze of empty classrooms. And that's when he hears the voices. Kids' voices crying for help. Voices coming from behind the classroom walls...