On August 13, 1995 about 1655 eastern daylight time, a Schweizer SGS 2-33A, a glider, N5750S, was substantially damaged, when it collided with trees, during the final approach at the Vansant Airport, Erwinna, Pennsylvania. The flight instructor and student pilot were not injured. Visual meteorological conditions prevailed for the local flight operated by Soaring Society of Princeton University. There was no flight plan for the personal flight conducted under 14 CFR Part 91. The flight instructor's stated that this was the second flight of the day with this student. The glider was towed to 3000 feet above ground level (AGL) and released. The student conducted airwork, and then returned to the airport for landing. The student entered the pattern on the crosswind leg at 1000 feet AGL. The instructor further stated: ...Entering base, it looked to me like we were on track for a normal landing. The dive brakes were still partially opened....We were not so high that we would need a slip in addition to dive brakes on final. I had another look for power and glider traffic, saw that we were clear and asked the student how our altitude was. He responded that we were high and immediately opened the dive brakes fully and put in a moderate slip. I said "No,"....The variometer was showing between 800 and 900 feet per minute down. I pushed the dive brakes shut and told the student to take out the slip.... ...I aimed for a notch in the trees, put in [a] crab to stop the side drift and fly along the line of the runway. Approaching the trees, the airspeed was down to 40 MPH, and there was no energy left to pull up the ten feet needed to clear. Both wingtips hit the trees. The glider turned sharply to the side.... Additionally, in the NTSB form 6120.1/2, the flight instructor reported that there were no mechanical malfunctions or failures with the glider.