The Maestro by Tim Wynne-Jones
Burl Crow hasn't had many breaks in his young life. His father is a manipulative lout with a dangerous temper; his mother, worn down by years of abuse, now resorts to her little helpers to get her through the days. Then he meets Nathaniel Orlando Gow, the Maestro, and in just one day, this eccentric genius changes Burl's life forever.