According to the flight instructor of the Schweizer 269C helicopter, the student pilot successfully performed three autorotations to a hover; however, during the fourth, he "landed hard with a yaw to the left." The flight instructor was not able to correct the yaw, and the helicopter impacted the ground, damaging the tail boom. The accident was not reported until the flight instructor was involved in a similar accident, in the same helicopter, about 30 days later. No mechanical deficiencies were reported by the flight instructor or the student pilot.