On October 27, 1999, approximately 0815 mountain daylight time, a Cessna 172B, N7906X, registered to and operated by the pilot, was substantially damaged when it departed the side of the runway and collided with a runway light during landing roll at Centennial Airport, Englewood, Colorado. The commercial certificated flight instructor and student pilot were not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the local area instructional flight being conducted under Title 14 CFR Part 91. The flight originated at 0800. According to the instructor, he was performing soft field touch and go landings with his student. During the third landing on runway 17R, a "gust of wind blew [the] aircraft" off to the left of the runway approximately 2 to 3 feet into the grass and impacted runway lights. The instructor was able to maneuver the aircraft back onto the runway, and he continued the flight lesson with his student for another hour. He stated that after the flight was concluded and they exited the aircraft, he observed a large hole in the horizontal stabilizer. At 0753, the wind was reported to be from 220 degrees at 9 knots. The instructor did not indicate on his accident report what the wind conditions were at the time the accident occurred.