On July 7, 2002, about 0950 eastern daylight time, a Piper J3-C65, N9264, was substantially damaged when it impacted the ground near Trinca Airport (13N), Andover, New Jersey. The certificated flight instructor was seriously injured, and the certificated private pilot received minor injuries. Visual meteorological conditions prevailed at the time. No flight plan had been filed for the local instructional flight, which was conducted under 14 CFR Part 91. The private pilot was receiving training for a tailwheel endorsement. According to the flight instructor, after completing a landing, the private pilot climbed the airplane to 600 feet above the ground, and turned crosswind. At 700 feet, the flight instructor reduced power to simulate an engine failure. The private pilot "kept pulling the nose up," and the flight instructor told him three times to "keep the nose down." The private pilot turned the airplane 90 degrees, towards the airstrip. He then let the airplane "get too slow and low," and the flight instructor took control of the airplane. As he did so, the airplane stalled and entered a right spin. The flight instructor recovered from the spin about 30 feet above the ground, added power, and saw trees ahead. He turned the airplane steeply to avoid trees. However, during the rollout from the steep turn, the airplane's left wing impacted the ground. The flight instructor further added that the accident occurred near the end of the instructional flight, and that the maneuver was the last one before the final landing. He also noted that the private pilot had successfully completed the maneuver three times during the same flight.