The flight instructor said he was giving the certificated private pilot some training in tail wheel aircraft. He told the pilot that the rudder pedals were very sensitive. The pilot taxied onto the runway, lined up on the centerline, and applied power for takeoff. The takeoff roll was normal until the tail wheel lifted off and the nose turned left. The flight instructor said the pilot overcorrected to the right and then back to the left. The flight instructor then got on the controls with the pilot, and, as the aircraft turned right a second time, the turn progressed into a ground loop. Subsequently, the left main landing gear separated from the fuselage and the left wing was bent up.