On October 23, 1996, at 1630 mountain daylight time, a Piper PA-18, N3939Z, was substantially damaged when the pilot lost control of the airplane during landing. The instructor pilot was unable to take control of the aircraft from the student pilot and prevent the aircraft from a ground loop. The 14 CFR Part 91 flight had departed the Alliance Municipal Airport, Alliance, Nebraska, on a local training flight. Visual meteorological conditions prevailed and no flight plan had been filed. The instructor pilot reported that the airspeed was a "little fast" during the landing transition. At touchdown the airplane started veering right, but then the student pilot overcorrected and the aircraft veered off the runway to the left. The instructor pilot reported that he came on the controls. He reported that the airplane entered a ground loop and the left wing impacted the ground.