The flight instructor of a tailwheel-equipped airplane reported that he was instructing the airplane's owner, who was also a private pilot, during a proficiency flight in gusty crosswind conditions. The flight instructor further reported that during the landing roll, the airplane began to weathervane left into the wind, and he took the flight controls from the private pilot. Subsequently, he reported that he "stopped a ground loop to the left, only to ground loop to the right." During the ground loop, the left wing impacted the runway and was substantially damaged. The flight instructor did not report any mechanical malfunctions or failures with the airplane that would have precluded normal operation. The automated weather observing system at the airport about 30 minutes before the accident recorded the wind at 210 degrees true at 8 knots, gusting to 13 knots. The flight instructor reported that the landing was on runway 31.