Immediately after liftoff, the flight instructor simulated an engine failure, and the pilot executed a rejected takeoff, landing on the remaining runway. When the tailwheel contacted the runway, it began to "shimmy violently and disengaged the steering pin." The airplane veered to the left, and the pilot was unable to stop the veer using the right rudder and brake. The airplane exited the left side of the runway while moving sideways to the right. The right main landing gear collapsed, resulting in substantial damage to the right wing. An examination of the tailwheel mechanism showed excessive wear in both the locking collar hole and the drag links in the tailwheel assembly. It was likely that the locking pin had become retracted from the locking collar on the tailwheel at some time during the takeoff or during the landing. Both pilots stated that they had locked the mechanism before takeoff and had good directional control of the airplane during the takeoff run.