PA-28 instructor pilot reported a loss of control during landing on a training flight resulting in a runway excursion. The instructor was unable to prevent the aircraft exiting the runway into the grass and damaging a taxiway light and a sign.

Narrative

On Day 0 I was conducting a lesson for student pilot on certain Private Pilot maneuvers to include takeoff and landing. The student had previously soloed under my direction and had not flown in approximately 5 weeks. During the later portion of the flight we were exclusively working on takeoff and landing and the first three landings were routine. On the fourth however we touched down for landing as normal and then while rolling began veering off the runway. I immediately tried to regain control of the Piper Warrior 2 but was unsuccessful in my attempt. This reaction time was partially delayed due to being distracted for a few seconds because I felt he was competent during the prior landings. In my attempt to regain control of the pedals I realized the student had 'frozen up' on a combination of rudder and brake control so I began trying to slightly hit his side stating 'let off.' In addition although I was able to reach the pedals and operate them with full range of motion I possibly could have had my seat up a bit further to help get leverage on the pedals. In this event we went into the grass and through a taxi-light. The Pitot Mast on the left wing also clipped the taxi sign causing damage. A contributing factor as well may have been the sun almost setting. Time of event was approximately XA:30 landing on Runway XX and sunset is approximately XB:22 local.