Teachers probably work fewer hours than most other folks (over the course of a year). The extent of the difference is likely less than many believe because many teachers work so many hours off the clock. That being said, the data is–frankly–crummy.
What has been measured is how many hours teachers are in front of students in the U.S. and in other countries. (Prep time, non-teaching duties, etc., aren’t included.) It appears from OECD data (Education at a Glance, 2012.) that American teachers already spend more time in front of students than almost anywhere else.