On April 4, 1994, about 1030 eastern daylight time, a Piper PA-28R-200, N30DW, was substantially damaged during a hard landing at the Windham Airport, Willimantic, Connecticut. The certified flight instructor and his dual student were not injured. Visual meteorological conditions prevailed. The local instructional flight was conducted under 14 CFR Part 91. The certified flight instructor reported that he and his student were practicing touch and go landings at several airports within the local flying area. He said a hard landing occurred at the Windham Airport, but he did not think the airplane sustained substantial damage. The certified flight instructor stated that upon termination of the flight, he noticed the airplane had sustained damaged and reported it to the Federal Aviation Administration (FAA). An inspection of the airplane by a FAA Safety Inspector revealed the airplane's wings, wheel wells, and "bottom false spar cap" sustained damaged.