The pilot reported that he was starting a formation flying clinic and that the purpose of the flight was to gain familiarization and proficiency in the airplane. After completing a flight in the local area, he returned to demonstrate several wheel landings. The landing touchdown was normal; however, the pilot lowered the tailwheel to the runway at a higher speed than usual. To reduce the load on the tailwheel, he reduced the back pressure on the control stick. The airplane started to drift to the right and his efforts to regain control were not successful. The airplane subsequently departed the right side of the runway into “relatively softer ground” adjacent to the runway. The left main landing gear “folded inboard at the oleo strut and the left wing contacted the ground.” The airplane sustained substantial damage to the left wing. The pilot reported no mechanical malfunctions or failures with the airplane before the accident. He noted that holding the control stick at the aft limit until the landing was complete might have prevented the accident.