According to the flight instructor, he and the student pilot were practicing maneuvers approximately 2,500 feet above ground level. The flight instructor decided to practice simulated engine failure procedures within the vicinity of the airport and turned the fuel selector to the "OFF" position. The student pilot trimmed the airplane for best glide speed, initiated a turn toward the airport, and then took time to locate the pilot operating handbook in order to follow the emergency procedure. In addition, the student pilot could not locate the exact position of the airport until the flight instructor directed him. The student pilot unsuccessfully attempted to restart the engine and the flight instructor took control of the airplane. Then, the flight instructor unsuccessfully attempted to restart the engine, and subsequently selected a field to land to perform a forced landing. During the landing, the nose landing gear impacted the ground, which resulted in substantial damage to the firewall. The student pilot/mechanic of the airplane reported no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation.