At about 1415 central time, a Cessna 152 crashed short of the runway at Olive Branch Airport when the flight instructor intentionally shut off the fuel as part of engine-out training. Neither occupant was injured. The instructor said he moved the fuel selector to the OFF position when the airplane was abeam the numbers on downwind. The student ran through the emergency procedures, but the engine did not restart when the fuel selector was returned to ON. The pilots did not immediately turn to the runway because of traffic on final, but flew a normal pattern. The airplane landed short and the nose gear collapsed, damaging the airplane.