I'm The King Of The Castle by Susan Hill

A spare, chilling psychological novel about a vulnerable young boy who moves with his mother to a large, isolated house and becomes the target of a relentless, escalating campaign of torment by a local boy; as the two children vie for control and status, the indifferent or self-absorbed adults around them fail to intervene, and the mounting cruelty drives the story toward a devastating, inevitable climax that exposes the corrosive effects of loneliness, power and parental neglect.