The pilot and owner of the tailwheel equipped airplane reported that he was performing a short field approach with a flight instructor. During the landing, the instructor took control of the aircraft and pulled the control stick back, to increase the airplane’s pitch, and did not increase engine power. The airspeed decayed and the airplane experienced an aerodynamic stall and landed hard. The flight instructor reported that the sport pilot/owner was at the controls during the short field approach, and he had been talking him through the approach. On final approach, the instructor told the pilot to lower the nose and add power. Subsequently, the flight instructor applied full engine power, however, the airplane landed hard, which resulted in substantial damage to the fuselage. The instructor and the pilot both reported that there were no preaccident mechanical malfunctions or failures that would have precluded normal operation.