During the instructional flight, the flight instructor and student pilot were practicing simulated engine failures in the airport traffic pattern. The flight instructor and student pilot reported that the airplane was configured for landing during the approach. The airplane landed with the landing gear retracted and came to rest on the runway. The flight instructor and student pilot were not injured. Examination of the airplane showed the rear wing spar cap was damaged during contact with the paved runway surface. During recovery, the landing gear was extended with no anomalies by operating the gear handle. The Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) was not received by the NTSB investigator-in-charge.