The pilot, who was the amphibious airplane’s owner and possessed single engine land and sea ratings, was receiving instruction on takeoffs and landings. The flight instructor reported that the approach to the runway was normal; however, the pilot flared too high. The instructor verbally commanded power, but the pilot did not respond appropriately, and the airplane landed hard on the runway. The left, front wheel separated, the airplane departed the runway surface, struck a trench, and came to rest inverted. There were no injuries. An inspector with the Federal Aviation Administration examined the wreckage and determined that the damage to the fuselage was substantial. The flight instructor reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.