The flight instructor reported that he and student departed about 1345 on a local flight to practice instrument approaches. About 1700, while returning to the destination airport and crossing the initial approach fix for a practice instrument approach, the left fuel tank indicator showed empty, and the right tank indicated about ¼ full (about 5 gallons remaining). About 6 miles from the runway, they felt a reduction in power, and the student announced the engine had lost power. The flight instructor took the controls and maneuvered the airplane to perform a forced landing to a field. They attempted to restart the engine, but the restart was not successful. During the forced landing, the airplane nosed over and came to rest inverted. The pilot estimated the total flight time was 3 hours and 15 minutes. Postaccident examination of the airplane revealed substantial damage to empennage, and the fuel line to the fuel pump inlet did not contain any fuel. During recovery, a few ounces were found in the fuel system. The fuel tanks did not appear to be compromised, and fuel seepage from the wings was not detected on the ground. The flight instructor reported that throughout the flight, the student properly leaned the engine during cruise, and the fuel flow indicator showed about 6 gallons an hour average consumption during those times. The RPMs read about 2,100 to 2,200, and the indicated airspeed was just over 100 knots. The airplane’s fuel capacity was 40 gallons, and prior to departure, the airplane’s fuel tanks were full. The installed engine was derated to 185-horsepower. Engine performance charts showed that at 195-horsepower, fuel consumption could be approximately 15.8 gallons per hour. At 75% power (about 157-horsepower), fuel consumption was about 12.6 gallons per hour. However, precise flight information was not available to confirm total fuel consumption for the accident flight.