In a written statement, the flight instructor stated that he and the pilot were practicing traffic pattern work and had performed two simulated engine failures prior to the accident. The instructor initiated a third simulated engine failure at a higher altitude than the previous two, and he suggested the pilot perform S-turns to lose altitude. While completing the turns to dissipate altitude, the airplane descended too low to complete a power-off landing to the runway. The instructor called for a go-around and attempted to add power, but the airplane pitched down and impacted the ground which resulted in substantial damage to the wings and fuselage. The flight instructor reported there were no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation. The instructor reported that he has had students mistake the pitch trim control for the throttle on past flights and after the accident they found the trim control pushed full forward into the nose down position.