PA-44-180 instructor reported a runway excursion while instructing the student on simulated aborted single engine takeoff procedures in the aircraft. The instructor simulated the aborted takeoff condition by applying rudder displacement and the student responded by locking the brake resulting in a loss of control on the runway. The aircraft looped 135 degrees from the takeoff position.

Narrative

Student's 3rd flight in a multi engine aircraft and 1st time preforming a simulated aborted take off with one engine inoperative. Aborted take off procedure was discussed during prebrief; idle throttles and maintain directional control with rudders and then brakes as necessary to return to centerline and call 'Aborting.' We also discussed the methods I would use for simulating single engine out such as either pulling one mixture or applying rudder to simulate the engine out. We had practiced aborted takeoffs in a previous mission in a simulator. In aircraft; during engine runup; I informed the student we would be setting up for a short field take off but she could expect a simulated one engine out to implement the aborted takeoff procedures. I did not inform the student which engine I would be simulating but planned for the left engine as it was on the non-taxi side of the runway.On the runway the student set up for a short field take off. As soon as she released the brakes I verified that the airspeed tape had no indication and applied left rudder. Student pulled throttles idle but also applied firm brakes. Brakes locked up and aircraft continued swerving to the left. I believe this was due to the left rudder input still being in place as the student became scared and applied brakes. I took controls while the aircraft was still on the runway but the aircraft was already passing through 50 degrees off centerline and continued to loop left towards the left side of the runway. I did not want to slam on the right rudder and risk the aircraft loosing control in the opposite direction or continue locking the brakes. I accepted that the aircraft would be leaving the runway and neutralized the rudders. Our aircraft stopped about 135 degrees from our take off position to the left. In retrospect I think I could have left my feet position hovering over the rudders instead of returning them to the floor after the initial left rudder input so I could have assisted remaining in the runway before it was too late.