I am looking for a YA book about a boy who learns to use powers from a mind-adept, in a seemingly abandoned house. The adept helps him open his mind by using a cube. One of his powers, I believe, is to go into dreams of people that he knows. He helps his young female neighbor friend by doing this, opening a door in her mind. He tries to open the mind-door of a local older bully, but finds out the young man can't be helped because he has been abused mentally and physically. I don't believe the book I read is past 1995. It might have the word "adept" in it.
Christopher by Richard M. Koff
Christopher is 13 and often too smart for his own good. He hates school and can’t seem to stay out of trouble. On a dare he knocks on a door to a house all his friends say is haunted and meets a strange, quiet man who calls himself the Headmaster.
The Headmaster starts Christopher on a series of lessons unlike anything he was taught in school. He learns how to move objects with his mind alone, how to read other people’s thoughts, he becomes invisible or shrinks to the size of a pencil.
It’s not just for fun. The Headmaster has a mission for Christopher that will change his life forever.