The flight instructor reported that he and pilot receiving instruction had performed eight takeoffs and landings without incident. The flight instructor’s procedure was to perform the checklist items and select landing gear down when established on downwind in the traffic pattern. During the final traffic pattern, they became distracted and did not perform the checklist. The pilot receiving instruction reported that they did not lower the landing gear during the final approach and the airplane landed wheels up. The airplane sustained damage to the lower fuselage structure during the landing. Video footage provided by the airport manager showed the airplane’s landing gear fully retracted during the approach. Neither pilot recalled hearing the landing gear warning horn prior to the gear up landing. The mechanic that recovered and examined the airplane after the accident reported that the landing gear extended normally, and the landing gear warning horn was audible.