Where does he work?

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."