On May 1, 1996, approximately 1800 Alaska daylight time, a wheel equipped Cessna 172 airplane, N3795L, registered to and operated by Smith Aero Services of Fairbanks, Alaska, experienced a hard landing causing damage to the firewall while performing touch and go landings at Fairbanks International Airport, Fairbanks, Alaska. The instructional flight, operating under 14 CFR Part 91, departed Fairbanks for a local flight. No flight plan was filed and visual meteorological conditions prevailed. The certificated flight instructor and the student were not injured and the airplane received substantial damage. During a telephone conversation with the flight instructor on May 24, 1996, she stated that during one of the landings the student flared higher than normal and the airplane struck the ground in a three point attitude. She felt that the landing was not unusually hard so they continued to perform touch and go landings. After the flight, the student, who had ten hours of total flight time, performed the walk around inspection and did not see any damage. The flight instructor did not perform the walk around inspection with the student. Approximately three days later, another instructor noticed that the control yoke would not move through its entire forward range of travel. Later examination showed that the firewall was bent and the surrounding structure was impeding the control yoke's movement. The flight instructor believes that they did not cause the damage because during the remainder of their flight they did not encounter restrictions during the control yoke's movements. However, the company records show that the airplane had not flown since their flight. The operator was sent an NTSB Form 6120.1/2 on May 28, 1996 and June 11,1996. The flight instructor stated she did not feel this was an accident and she did not complete and return the NTSB Form 6120.1/2.