Dreamwalker: The Second Plain by Charles W. Jones
Saul can control dreams, not just his dreams but dreams of people he comes in contact. At first, he is not aware of what he can do and does not understand why people act strangely when he gets angry. When he goes away to boarding school he inadvertently calls for help from his Spirit Guide, Gappé.
Gappé teaches Saul about his gift and alerts him about danger from the Man who wants the gift. His paranoid warnings turn out to be true when the Man finds Saul after he is finished with...