Flight instructor on training flight with student reported loss of control due to autopilot inadvertently activated by student. Flight crew returned to departure airport and landed.

Narrative

On a training flight with a student in a C172 ASEL; I experienced an autopilot anomaly. While training doing normal maneuvers (ground reference); my student inadvertently hit the autopilot rocker switch (located directly below the throttle) engaging the autopilot. Neither student or I immediately recognized activation (there are no annunciations or illuminations that display it has been activated). My student then turns to me and states 'something feels wrong; I can't control the plane.' Upon hearing this; I take control over the aircraft and immediately feel the autopilot has been activated; and the plane is trying to turn. I am still unsure in what fashion/function the autopilot was in; but the plane was trying to bank fairly aggressively to the right. I turned the rocker switch to 'off' but the autopilot did not disengage. Being very close to ZZZ; I made the decision to immediately turn back to the airport and contact Tower as I was still 'fighting the autopilot.' Upon initial contact with Tower; I communicated a request for priority handling with minimal turns as we were experiencing a flight control anomaly . Tower coordinated with me to setup on a wide right downwind to base for Runway XX into ZZZ. Upon running descent checklists and still trouble shooting the autopilot while flying inbound; I located the breaker associated with the system and pulled it. After I pulled it; the plane banked abruptly to the left; close to about 60 degrees; as a result of the excess control pressure I was exerting to compensate. After regaining level flight; we turned final for the runway into ZZZ and executed a no flap landing as I was still unsure of what was happening with the aircraft. I communicated my intentions of doing so with Tower for traffic considerations as the landing was going to be longer than normal. I executed the landing normally; and returned to the flight school. After shutdown and debrief; me and the flight school owner went out to the aircraft to troubleshoot the error to see if we could replicate the events. After several minutes of testing; the autopilot switch worked by design; disengaging properly every single time. We were not able to replicate the anomaly I experienced in the air. Upon reflection of this event; I could have been more prudent in pulling the breaker associated with the autopilot as that is the proper course of action in this event. Ultimately; returning to the airport was the correct course of action.