On January 13, 2001, about 1630 hours Pacific standard time, a Piper PA-22-150, N3854P, owned and operated by the student, ground looped during landing at the Castle Airport, Atwater, California. Visual meteorological conditions prevailed, and no flight plan was filed for the instructional flight. The airplane was substantially damaged, and neither the certified flight instructor (CFI) nor the student pilot was injured. The local flight was performed under 14 CFR Part 91, and it originated from Atwater about 1540. According to the student, he possessed a commercial pilot certificate but had no experience flying the PA-22-150 airplane that he had recently purchased. The airplane had been modified by installation of conventional landing gear. The student additionally reported that he had about 5,000 hours of flight time. However, his experience in the tail wheel equipped PA-22-150 was 2 hours. The CFI reported that he had 3,469.7 total hours of flight time. His experience in the airplane was 5 hours. The student also stated that he had hired the CFI to check him out in the airplane. After flying in the traffic pattern and successfully performing a series of takeoffs and 3-point landings, he attempted to perform a wheel landing. The student stated that a wind gust was encountered as the airplane decelerated on runway 31. (Runway 31 is 11,802 feet long and 300 feet wide.) The student indicated that he was unable to maintain directional control, and the airplane veered left. Following the collapse of the right main landing gear, the right wing contacted the runway surface and broke. The CFI reported that his student was on the controls at the time of the gust encounter, loss of control, and ground loop. In the CFI's completed accident report, he indicated that at the time of the accident the local wind was from the southwest at 10 knots, with 15-knot gusts. At 1553, the Merced, California, airport, located about 7 miles from Atwater, reported its surface wind was from 280 degrees at 4 knots.