According to a telephone conversation and the Pilot Aircraft Accident report submitted by the flight instructor, he and his private pilot student were conducting a "currency flight" and the instructor had just finished demonstrating a 180 degree autorotation. The student was performing a second 180 degree autorotation. The instructor stated that at 200 feet above ground level, the student brought power on; however, the rotor rpm was low. The instructor stated that the student brought the "collective up" and the rotor rpm continued to drop. The helicopter impacted the runway in a "high rate of descent", spreading both landing skids out laterally and "denting" the tail boom. The instructor reported no anomalies with the helicopter or its systems. An examination of the helicopter's systems, conducted by the FAA, revealed no anomalies.