Where does he work?

A grade school teacher was asking students what their parents did for a living. "Tim, you be first. What does your mother do all day?" Tim stood up and proudly said, "She's a doctor." "That's wonderful. How about you, Amy?" Amy shyly stood up, scuffed her feet and said, "My father is a mailman." "Thank you, Amy" said the teacher. "What does your parent do, Billy?" Billy proudly stood up and announced, "Nothing. He's an economist."