The pilot of the glider was receiving a biennial flight review from a flight instructor. They completed two uneventful flights prior to the accident flight. According to the flight instructor, during the third flight, with the pilot under evaluation at the controls, the glider was approximately 500 feet above the ground, 2,000 feet from the end of the turf runway, and slightly slow in the flight instructor's judgment. To correct for the airspeed deficiency, the flight instructor manipulated the flight controls forward and told the pilot to increase the airspeed due to the strong headwind. According to the pilot, the airspeed varied 15 mph during the approach and the glider was descending fast, when he relinquished control of the glider to the flight instructor. The flight instructor stated that he did not assume control of the glider, which was abnormally low but still within a good safety margin to land, in his judgment. About 200 feet above ground level, the glider encountered a downdraft for approximately four seconds. Then, when the glider was 75 feet above ground level, it banked violently to the right. The glider impacted trees, a berm, and a guard rail resulting in substantial damage to the fuselage and empennage. The flight instructor further stated that he never had any doubt that the pilot was in control of the glider, while the pilot under evaluation asserted the instructor stated he had control after the plane began a rapid descent on final approach. Both pilots reported there were no preexisting mechanical anomalies with the glider. The wind reported at an airport 10 miles to the southeast of the accident location was from 220 degrees 14 knots gusting to 21 knots.