The flight instructor (CFI) who has 4 total hours as a CFI was conducting an instructional flight with a student pilot. The student pilot made 3 touch and go landings to runway 21. The surface winds at the airport were 200 degrees at 12 knots. The CFI stated the student did not maintain airspeed resulting in a sink rate on the previous approaches. He instructed the student to conduct a short field approach with an obstacle. The student conducted the before landing check, lowered the flaps to the first notch and turned on base. The student lowered flaps to the full down position, turned final, and continued the approach. The airplane descended to 25 feet over the runway when the airspeed decreased and the airplane entered a vertical rate of descent. The student pilot did not apply power. The CFI reached over to add power, missed the throttle, flared the airplane, and it collided with the runway hard resulting in structural damage to the airframe. No mechanical problems were reported by the CFI.