Skyhawk 172/Cutlass 172
Flight Crew Commercial; Flight Crew Flight Instructor
Flight Crew Last 90 Days 75; Flight Crew Total 4500; Flight Crew Type 4500
Communication Breakdown; Situational Awareness
Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Runway
General None Reported / Taken
Human Factors
Student could not stop the plane and over ran the end of the runway by about 20 feet.  No damage or injury. Should have told student to go-around and since he did not; I should have lifted the flaps to gain more runway stopping action.
C172 instructor reported landing long resulting in a runway excursion.