The flight instructor reported that the wind was calm when the pilot receiving instruction performed a 3-point landing in the tailwheel equipped airplane. During the landing roll, the tailwheel began to shimmy. The pilot was able to raise the tail momentarily in an attempt to stop the shimmy before it settled back onto the runway. The tailwheel continued to shimmy, and the airplane veered to the left. The pilot attempted to correct with right rudder and brake input. The airplane began to correct to the right towards the runway centerline, however, the right turn continued to accelerate, despite the pilot and flight instructor’s left rudder inputs. Subsequently, the left main landing gear collapsed, and the left wing was substantially damaged when it impacted the ground. Post accident examination of the airplane determined that the tailwheel leaf spring assembly was loose. Corrosion was observed on the left main landing gear attach points. It is likely the loose tailwheel spring assembly was preexisting and caused the tailwheel shimmy and contributed to the loss of directional control and the subsequent landing gear failure.