Most good tutors would probably be working around 20 hours a week, with an additional 10-20 hours of unpaid preparation time. This explains the disparity with teacher salaries.
I don't think this does explain the disparity. Most core teachers I know also have an additional 10-20 hours of "unpaid" prep time. (Time outside that 40 hours, anyway.)
I think the disparity is more reflected in the relative value of one-on-one instruction vs. what you typically see in a classroom (closer to 30:1).
