At 16:00 MST, a Cessna 172N was damaged during a forced landing in rough terrain 15 miles west of Prescott. The flight instructor and dual student were not injured but the airplane was substantially damaged. The flight schools safety officer said the flight instructor and student were conducting a simulated engine failure from approximately 3,500 feet agl when the student inadvertently shut the fuel selector off without the flight instructor noticing. At 500 feet agl, the flight instructor asked the student to do a go-around. There was no response when full throttle was applied, so the instructor took the controls and performed an emergency landing.