On July 12, 1998, at 1100 eastern standard time (edt), a Schweizer SGS 2-33A, N17901, piloted by a Certified Flight Instructor (CFI), sustained substantial damage when it collided with a taxiway light during landing roll on runway 18 (5000' x. 100', concrete, dry) at Indianapolis Terry Airport, near Indianapolis, Indiana. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 instructional flight was not operating on a flight plan. The CFI and student reported no injuries. The local flight departed Indianapolis Terry Airport at 1055 edt. According to the pilot-in-command's written statement, he was giving dual instruction to a student pilot at the time of the accident. The CFI stated that when they were maneuvering the aircraft to enter the traffic pattern for the grass area, which parallels runway 18, he noticed that another glider was also entering the same traffic pattern. The student pilot initiated a radio transmission to the pattern traffic that they intended to execute a left pattern for the grass landing area. The CFI also made a transmission to the other glider that they were directly behind them. The CFI stated that there was no response. The CFI decided to alter their traffic pattern to land on runway 18, due to the other traffic that was ahead of their glider. The CFI stated that when they turned base to final they were approximately 250' above ground level (agl). The CFI told the student to use "Full" spoilers to bring the aircraft back on a normal glide path to the runway. The CFI stated that at approximately 100' agl the student had "Full" spoilers deployed and had an excessive nose down attitude. The CFI told the student "Close" the spoilers and bring the nose up to reduce the excessive airspeed. The CFI stated that the student began to bring the nose up, without closing the spoilers, and that he took control of the aircraft at this point. The CFI closed the spoilers completely but the aircraft was already entering a stall. The CFI stated that he reduced the angle of attack in order to regain airspeed and then flared close to the ground. The CFI stated that the aircraft "Pancaked-in, a landing hard enough to throw me into the shoulder straps and my head down so that briefly I could not see outside." The aircraft drifted to right side of the runway and the right wing impacted a runway light before coming to a stop. In the written statement by the pilot in command, the CFI stated, "My errors were not taking control earlier and not announcing to the student that I had done so when I grabbed the controls."