The owner, seated in the forward seat was receiving recurring flight instruction from the certified instructor (CFI) seated in the rear seat. After takeoff the flight proceeded to Culpeper Regional Airport where the flight entered the traffic pattern for runway 04. The flight turned onto final approach and the owner reported that with a right quartering headwind of 4 knots, the airplane crossed the threshold at the recommended approach speed (50 miles-per-hour). The owner initially reported the tailwheel equipped airplane touched down in a left wing low attitude, while the CFI initially reported that the owner touched down in a three-point attitude when a swerve to the right developed. He assisted verbally and helped with the rudder and brakes then took control, but the airplane ground looped to the right travelling into a ditch. Neither pilot reported a pre-impact mechanical failure or malfunction. Postaccident inspection of the airplane revealed substantial damage to the left wing. A surface observation weather report taken at Warrenton-Fauquier Airport (HWY), Warrenton, Virginia, on the day of the accident at 1455, or approximately 10 minutes after the accident indicates the wind was from 120 degrees 5 knots, no gusts were reported. The HWY airport is located about 8 nautical miles and 062 degrees from the Culpeper Regional Airport.