Betty G. Birney 
School According to Humphrey 

Join much-loved Humphrey the hamster for a new adventure! After a fur-raising holiday at Camp Happy Hollow, Humphrey returns to Room 26, eager to see his old friends. He is shocked to find the classroom full of strangers, like Rolling Rosie, Hurry-Up-Harry and Forgetful Phoebe. Where have all his old classmates gone? But the charming Humphrey soon learns that these new students could really use a helping paw from their classroom pet. In the end, even a small hamster can never have too many friends!