The flight instructor reported that while his student was at the controls, he initiated a simulated engine failure, and the student executed the emergency procedures for a forced landing. The student chose a place to land and configured the airplane for landing, including full flaps. The instructor noticed that the airplane’s airspeed was “a little slow”, and he instructed the student to check the airspeed, then recover from the simulation. The student retracted the flaps instead of adding engine power, and the airplane stalled and sank. The instructor immediately attempted to take over the airplane’s controls from the student and verbally commanded “my controls”, but the student was “stuck on the controls and locked up.” The airplane continued to descend and touched down in a field and nosed over. Both wings, the fuselage, the vertical stabilizer, and the rudder sustained substantial damage. The instructor reported that there were no preaccident mechanical malfunctions or failures that would have precluded normal operation.