The flight instructor stated that the purpose of the flight was for the private pilot/owner to receive instruction for the tailwheel endorsement. After practicing several successful takeoffs and landings, the flight instructor had the private pilot set-up for a full stop wheel landing to runway 16, which had a six knot, 45 degree crosswind. While in ground effect, the private pilot reduced the throttle too fast, which increased the sink rate and the aircraft touched down firmly on the mains. The private pilot arrested the bounce with forward pressure before the aircraft lifted off, and applied some power to maintain directional control. The aircraft then began to make an excursion from the runway centerline and the private pilot lowered the tail which made the aircraft unstable. The flight instructor then assisted the private pilot and stabilized the aircraft. The private pilot then indicated that he could handle the situation, and the flight instructor returned control back to the private pilot. The flight instructor stated that he may have returned control back to the private pilot too quickly, as the situation degraded to large excursion from centerline, and the aircraft diverted from normal track. The flight instructor was not able to regain directional control and the aircraft ground looped to the left. During the ground loop, the right wing and elevator contacted the ground and were structurally damaged.