Skyhawk 172/Cutlass 172
Flight Crew Flight Instructor
Aircraft Equipment Problem Less Severe; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Taxiway
Aircraft Aircraft Damaged; General Flight Cancelled / Delayed
Aircraft
Upon completion of required engine start up checklist; my student took over control and started out of [the] ramp to Runway XX. While student started to taxi aircraft to Taxiway; he told me he was having a difficulty to taxi with his left rudder with power setting at [approximately] 800 RPM. I told the student to readjust his seat to forward to allow him to proper steering the aircraft on the ground. After reaching to Taxiway; student had a very hard time to maintain taxiway center line and started to yaw to the right with power idle. I immediately took over the control and applied full left rudder pressure with left brake but it did not work well on my side either. Aircraft started to yaw off taxiway and stopped on the grass area.After this incident occurred; I was told by my student that both of us were applying full left rudder pressure to prevent aircraft steering to the grass; but it failed to respond and aircraft went straight to the grass; Prop strike hitting taxiway light.
C172 flight instructor reported the aircraft was uncontrollable using rudder pedal steering resulting in a prop strike.