The flight instructor reported that, during the takeoff climb from a grass runway with the student pilot flying, about 25 ft above ground the "climb rate became stagnant." He added that he instructed the student to "lower the nose slightly," but after "several seconds the airplane did not resume a normal climb rate." The flight instructor took the flight controls and noticed that they were "sluggish" and it felt as if the airplane was caught in "wind swirls" and downdrafts. Subsequently, the flight instructor made a "small left turn" toward a small gap in the tree line ahead and the airplane impacted a heavily wooded/treed area.The fuselage and both wings sustained substantial damage. The flight instructor reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.According to the flight instructor, the airplane departed "loaded at gross weight." The student pilot reported that the flight instructor did not discuss weight and balance with him before flight.During postaccident interviews with the National Transportation Safety Board investigator-in-charge, the student and flight instructor each reported their personal weight and a total of 10 gallons of fuel on board at takeoff. Based upon the information provided, the takeoff weight was 1,389 lbs, which was 139 lbs over the maximum gross weight (1,250 lbs) published in the airplane Pilot's Operating Handbook. The airplane's center of gravity for takeoff was within limits at 18.65 (12.4 to 22.0). An automated weather observation station 8 nautical miles (nm) southwest of the accident site reported that, about the time of the accident, the wind was from 200° at 5 knots, temperature 82°F (28°C), dewpoint 54°F (12°C), and barometric setting of 29.76 inches of mercury. The calculated density altitude 8 nm southwest was 2,648 ft. The flight instructor reported that they took off from runway 20, which was 2,600 ft long. Page 2 of 7 GAA17CA347According to the Federal Aviation Administration (FAA) Koch Chart, when considering the surrounding temperature and field elevation, the airplane would have likely experienced a 30% increase to the normal takeoff distance and a 25% decrease in the normal climb rate. The airplane's POH did not publish takeoff performance information.The FAA Pilot's Handbook of Aeronautical Knowledge stated, in part: Effect of Weight on Flight Performance The takeoff/climb and landing performance of an aircraft are determined on the basis of its maximum allowable takeoff and landing weights. A heavier gross weight results in a longer takeoff run and shallower climb, and a faster touchdown speed and longer landing roll. Even a minor overload may make it impossible for the aircraft to clear an obstacle that normally would not be a problem during takeoff under more favorable conditions.Runway Surface and Gradient Runway conditions affect takeoff and landing performance. Typically, performance chart information assumes paved, level, smooth, and dry runway surfaces. Since no two runways are alike, the runway surface differs from one runway to another, as does the runway gradient or slope. Runway surfaces vary widely from one airport to another. The runway surface encountered may be concrete, asphalt, gravel, dirt, or grass. The runway surface for a specific airport is noted in the Chart Supplement U.S. (formerly Airport/Facility Directory). Any surface that is not hard and smooth increases the ground roll during takeoff. This is due to the inability of the tires to roll smoothly along the runway. Tires can sink into soft, grassy, or muddy runways. Potholes or other ruts in the pavement can be the cause of poor tire movement along the runway.It is likely that the airplane was unable to clear trees at the end of the runway due to the decrease in takeoff performance, which resulted from the high-density altitude, the turf runway, and a takeoff weight over maximum gross weight.