The certified flight instructor (CFI) was demonstrating a power off spot landing to the dual student. The student held a commercial pilot certificate and was observing the maneuver at the time of the accident. The CFI stated that he made one attempted power off spot landing that ended in a go-around because the airplane would not have made it to the runway. He stated that on the second attempt, he again would not make it to the 1,000 foot runway markings he was aiming for, but felt that he would make it to the runway. The CFI stated that he started to add engine power when the airplane was about 30 feet from the runway end and 10 feet above the ground, but it "dropped into the sod." The airplane's left landing gear separated from the wing, and the left wing separated from the fuselage. The CFI reported no mechanical failures or malfunctions.