The flight instructor reported that the pilot receiving instruction was able to maintain an approximately 3° glide path on final approach to land, with power at an intermediate setting. However, on short final the airplane began to sink. The instructor stated that initially the pilot receiving instruction appeared to be adequately correcting, adding power, and increasing pitch. However, less than 100 ft above the touchdown zone and right before the flight instructor was about to command a go-around, the airplane sank further and touched down just prior to the runway. The right main landing gear impacted the edge of the runway and collapsed, substantially damaging the right wing. The flight instructor reported that there were no mechanical failures or malfunctions with the airplane that would have precluded normal operation.