C172 INSTRUCTOR HAS A RWY EXCURSION.

Narrative

I WAS INSTRUCTING A STUDENT PLT IN NO-FLAP LNDG PROCS. AFTER REQUESTING THE FULL LENGTH OF RWY WE WERE CLRED TO LAND AND I CONFIGURED THE PITCH AND PWR FOR AN EXTENDED GLIDING STRAIGHT-IN APCH-TO-LAND. UPON XING OVER THE ARPT BOUNDARY FOR LNDG; I REALIZED THAT I HAD MISJUDGED THE TIMING OF THE PWR REDUCTION DURING THE GLIDE; AND WAS STILL TOO HIGH AND TOO FAST TO TOUCH DOWN WITHIN THE FIRST 1/3 OF THE RWY LENGTH. I OPTED TO CONTINUE THE DSCNT AND USE THE FULL LENGTH OF THE RWY SINCE I WAS GOING TO MAKE A FULL-STOP LNDG ANYHOW. AT THIS POINT I ALSO CHOSE NOT TO EXTEND THE FLAPS IN AN EFFORT TO SLOW DOWN AS IT WOULD HAVE EXTENDED THE LNDG FLARE; AND ALSO DECIDED NOT TO EXECUTE A FORWARD SLIP SINCE I WAS TOO CLOSE TO THE RWY SURFACE BY THAT TIME. I TOUCHED DOWN WITHIN THE LAST 1/3 OF THE RWY AND APPLIED STEADY; FIRM BRAKING WITH FULL UP-ELEVATOR; BUT SOON REALIZED I WAS NOT GOING TO BE ABLE TO CLR THE RWY AT TXWY E WITHOUT EXCESSIVE SKIDDING AND TURNING. I THEREFORE CHOSE TO CONTINUE STRAIGHT AHEAD TOWARDS THE GRASSY RWY OVERRUN AREA IN ORDER TO MAXIMIZE FORWARD BRAKING; AND AVOID FURTHER INCIDENT THAT COULD HAVE RESULTED FROM A SHARP FAST TURN OFF OF THE RWY. I CAME TO A FULL-STOP AT THE END OF THE RWY; WITH THE MAIN WHEELS STILL ON THE PAVEMENT; BUT THE NOSEWHEEL WAS POSITIONED APPROX 4 FT INTO THE GRASS. THE NOSE OF THE AIRPLANE WAS POSITIONED BTWN A RWY END LIGHT AND THE TXWY E DIRECTION SIGN WHEN IT CAME TO A FULL-STOP; BUT NO PART OF THE AIRPLANE CAME INTO CONTACT WITH EITHER OF THESE OBJECTS.