The  flight instructor reported that the purpose of the flight was for the pilot undergoing instruction to perform touch-and-go practice takeoffs and landings. During the approach, the airplane was slightly fast and touched down about halfway down the runway. The instructor thought the pilot could still successfully complete a takeoff and monitored him as he retracted the flaps. As the airplane continued down the runway, the instructor decided that the airplane’s climb performance would not be sufficient to clear obstacles at the end of the runway and he opted to abort the takeoff. The instructor retarded the throttle lever to the closed position and told the pilot to apply maximum braking pressure. The airplane subsequently went off the end of runway into a grass field and continued about 100 feet before impacting a chain-link fence. During the accident sequence, the wing spar was substantially damaged. The airplane’s brake pedals were only accessible to the left-seated person, which is where the pilot was positioned. The instructor reported no mechanical malfunctions or failures with the airplane that would have precluded normal operation. He additionally stated that this accident could have been prevented by making a timely decision to go around when it was apparent that the airplane was going to touchdown further down the runway.