Planet of Junior Brown by Virginia Hamilton

[Aladdin] Junior Brown is a musical prodigy losing touch with reality and everyone around him—except for one important friend. Junior Brown is different than the other kids in his eighth-grade class. For one, he weighs three hundred pounds. He’s also a talented musician with a serious future as a professional pianist—if he survives middle school. With an overbearing mom, disappointed teachers, and fellow students who tease him mercilessly, Junior starts to slip away into his own mind. His last hope may be his only friend, Buddy Clark, a boy in his class without a home or family who has already learned some of life’s toughest lessons. Together, they find refuge and a creative outlet with the sympathetic janitor Mr. Pool, but when their secret cellar room is discovered, will the boys make it through the fallout?