PA-34 Flight Instructor reported that the student pilot retracted the landing gear instead of resetting the wing flaps; resulting in a gear collapse on the runway. Pilots secured the aircraft and evacuated without injury.

Narrative

We departed from ZZZ1 on Day 0 at XA:44 local time; en route to ZZZ under flight following with ZZZ1 Approach at 2500 feet VFR. Our flight to ZZZ was to refuel the aircraft and conduct the necessary preflight actions for our return to our home base airport; ZZZ2.Weather Conditions:Temperature: 23°CDew Point: 21°CWind: 180° at 4 knotsVisibility: 10 statute milesClouds: Broken at 18000 feet; scattered at 4600 feet; few at 2600 feet.After listening to the AWOS for ZZZ; we decided to use runway XX; as it provided a slight headwind component of approximately 3 knots and is the longest runway at the airport; measuring 8001 feet by 150 feet. Performance calculations indicated that we would require only 600 feet for landing.Following our descent checklist; we descended 15 nautical miles northwest of the field; visually approaching runway XX. Upon visual contact with the airport; we squawked XXXX and discontinued the flight following. We completed our pre-landing checklist; which included turning on the landing lights; setting 10 degrees of flaps; lowering the landing gear doing the call out: 'Three green' and verifying the gear position with the mirror on the inner side of the engine. As we progressed through flap settings of 20 and 45 degrees; we were doing the callout of 'three greens' to ensure the landing gear was down and secured. The student was at the controls and was following my instructions properly during a safe approach to the runway. The airplane touched down safely in the center of the runway without incident at XB:00 AM local time.As we were practicing a short-field landing as specified on the POH. I instructed the student to raise the flaps and apply brakes; he mistakenly placed the gear selector in the 'up' position. I quickly intervened; returning the lever to the 'down' position; but I noticed the airplane beginning to tilt to the left. I promptly took control of the aircraft and applied the necessary inputs to maintain runway alignment. After securing the airplane; I confirmed that the nose gear and right main landing gear were locked; while the left gear had retracted due to the incorrect gear lever input.Following the checklist to ensure the aircraft was secured properly; both the student and I evacuated without injury. After the incident; I contacted the Flight Service Station to inform ATC and close the runway to prevent hazards for other aircraft. I adhered to the instructions from FSS and later from the airport manager. The aircraft sustained minor damage to the propellers and belly. After airport operations lifted the aircraft; the gear was secured properly after recycling the gear lever.