The flight instructor reported that he had demonstrated a simulated engine failure and recovery at altitude to the pilot-under-instruction (PUI), and he subsequently asked the PUI to perform a simulated engine failure and recovery. Operating over an open field, the flight instructor allowed the pilot to descend over the field, and he recalled instructing the pilot to "Recover" and abort the landing about 200ft AGL. Failing to do so, the flight instructor came on the controls about 50 knots airspeed and about 100ft AGL, the airplane stalled, collided with the ground, and subsequently nosed over. The airplane sustained substantial damage to both wings and the engine mounts. The flight instructor reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.