The certified flight instructor was providing instruction to the private pilot, who was training for a commercial rating. While practicing a 180-degree autorotation, a downdraft was encountered approximately 200 feet above ground level (agl). The flight instructor stated, "I said that I had [the] controls and proceeded to bring back the power at about 150 feet agl. Everything was good; rotor and engine rpm were in the green. I pulled collective up as I've done in previous situations, but this time it was different. I pulled collective, but it was almost as if the helicopter couldn't fly out of it." The helicopter subsequently landed hard, which resulted in the tail boom being severed and the aircraft coming to rest on its right side. There was no post-accident fire, and no anomalies were reported with the helicopter.