On June 16, 2004, at 1720 eastern daylight time, a Schleicher ASK-21, N21VT, was substantially damaged during an off airport landing in Warren, Vermont. The two certificated private pilots received minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the instructional flight conducted under 14 CFR Part 91. According to the pilot-in-command, the purpose of the flight was to practice cross-country gliding techniques. The pilots departed from the Warren-Sugarbush Airport (0B7), Warren, Vermont, flew about 40 miles to the north, then 20 miles to the southeast, and finally 25 miles to the southwest to return to the airport. The lift was both thermal and ridge lift, with the glider experiencing an average maximum height of 2,800 feet above the ground. After flying for approximately 2 hours, as the pilots were returning to the airport, the wind "went southwest at 5 knots," decreasing the available lift. Approximately 4 miles from the airport, it became apparent that they were too low to make it to the airport, and they chose a field to land in. While on approach to the field, "persistent sink" made attaining the field "marginal," and it became necessary to increase the pitch of the glider to clear a 15-foot tall tree. As a result, the glider stalled and "mushed" to the ground. The winds reported at the Edward F Knapp State Airport (MPV), Montpelier, Vermont, at 1651, were from 330 degrees at 7 knots.