Student stalls an SGS 1-23 after changing his aiming point twice on final

A student pilot was seriously injured, though the SGS 1-23 was only lightly damaged, when he stalled while landing at Chouteau. Finding another glider parked on RWY 18, he radioed that he would land on the grass beyond it. His instructor, watching from the ground, radioed "land short"; the student took this to mean short of his chosen point and began a forward slip, then learned the instructor had meant behind the parked glider. He tried to stretch the glide back to his first point, judged he would not reach it, and opened the brakes to land shorter instead. A gust dropped away, the glider lost speed and sank rapidly, and it landed hard.

1. Glider parked on the runway: On approach to RWY 18 the student found another glider parked on the runway.
2. Instructor radios "land short": The student radioed that he would land on the grass beyond it; the instructor, on the ground, radioed "land short".
3. Student slips off height: Taking this to mean short of his chosen point, the student began a forward slip.
4. Instruction clarified, glide stretched: The instructor clarified that he had meant behind the parked glider, and the student tried to stretch the glide back to his first point.
5. Opens the brakes to land shorter: Judging that he would not reach his first point, the student opened the dive brakes and spoilers.
6. Loses speed and lands hard: A gust dropped away, the glider lost speed and sank rapidly, and it landed hard; the student was seriously injured.