The flight instructor demonstrated a simulated engine failure to his student while the airplane was on the crosswind leg in the traffic pattern. He reported that he attempted to land on the opposite runway from which they departed. He reported that while maneuvering to final approach the airplane was pushed to the left of the runway over a grassy area by a “sudden downward draft.” The flight instructor stated that he thought the airplane encountered “windshear coming down between the trees.” He landed the airplane in the wet grass between the taxiway and the runway, which resulted in a propeller strike. Post-accident examination revealed substantial damage to the engine mount. The flight instructor reported that there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation. The flight instructor reported that the wind at the time of the accident was 300° at 10 knots. The landing was made toward runway 10 which resulted in a 9-knot tailwind.