In a 2001 book, "Identifying Child Molesters," the psychologist Carla van Dam tells the story of a young Canadian elementary-school teacher she calls Jeffrey Clay. Clay taught physical education. He was well liked by his students, and often he asked boys in his class to stay after school, to do homework and help him with chores. One day, just before winter break, three of the boys made a confession to their parents. Mr. Clay had touched them under their pants.