People tend to perform at the level others expect of them, which has been shown with students, soldiers and employees. It is unusually strong at camp. Tell a swim instructor that a particular child is about to improve, and the child improves. The quietest version is the most useful one: mention to a struggling new counselor's supervisor that you see something special in her, then let the supervisor go find it.
This is the short version. The full lesson, with the story behind it, is in the book.
Take The Summer Camp MBA with you, or get the field notes by email while you work through the lessons here.