The pilot and flight instructor had been flying for over two hours, doing air work and making touch-and-go landings at Bridgeport (XBP), Alliance-Fort Worth (AFW), Meacham (FTW) and Hicks Airports (T67). Returning to XBP, they were making a final touch-and-go landing when the engine lost power. Unable to glide back to the runway, the flight instructor made a forced landing in a plowed field north of the airport. The airplane touched down hard, shearing off the landing gear, and sliding 60 feet before coming to a stop. The firewall was buckled. The flight instructor and pilot sustained minor injuries. A Federal Aviation Administration (FAA) inspector examined the airplane and reported the fuel selector was positioned on the left fuel tank. When electrical power was applied, the left fuel gauge registered empty. One quart of fuel was drained from the left fuel tank. The right fuel tank had not been compromised and contained fuel.