A C172 INSTRUCTOR AND STUDENT PLT MADE A TKOF FROM LEB WITHOUT A CLRNC.

Narrative

THE FLT STARTED OUT NORMALLY; THE STUDENT DID THE PREFLT AND EVERYTHING CHKED OUT OK. WE THEN LISTEN TO THE ATIS AND RECEIVED TAXI INSTRUCTIONS TO THE ACTIVE RWY (RWY 18). WHILE WE COMPLETED THE BEFORE TKOF CHKLIST; THE WIND CHANGED DIRECTION. TWR DIRECTED US TO USE THE RWY TO TAXI TO THE OTHER END FOR TKOF (RWY 36). I TAXIED DOWN TO THE OTHER END AND TOOK OFF. I NEVER CONTACTED THEM AGAIN BEFORE I TOOK OFF. NO OTHER AIRPLANES WERE IN THE VICINITY. THE STUDENT IS A NEW STUDENT THAT ALWAYS HAS A LOT OF QUESTIONS. ONE QUESTION ALWAYS LEADS TO ANOTHER; SO THERE CAN BE SOME FAIRLY LONG DISCUSSIONS ON A LARGE NUMBER OF SUBJECTS. WHILE WE WERE TAXIING ON THE RWY; SHE STARTED TO ASK ME A NUMBER OF QUESTIONS UNRELATED TO THE ACTUAL TKOF. BY THE TIME WE REACHED THE OTHER RWY AND GOT SET UP FOR TKOF; I WAS SO REMOVED FROM THE SIT THAT I DID NOT CONTACT THE TWR. HOWEVER; I DID PERFORM THE LINE-UP CHKLIST (LIGHTS ON; XPONDER ON). I REALIZED THIS AT ABOUT 500 FT ABOVE THE RWY. I TALKED TO THE TWR ON THE RADIO AND IT DID NOT SEEM LIKE THEY EVEN NOTICED. NOTHING WAS EVER SAID ABOUT IT. BEFORE OUR NEXT FLT; I SAT DOWN WITH THE STUDENT AND WE HAD A DISCUSSION ABOUT WHAT HAPPENED AND HOW TO AVOID IT IN THE FUTURE. WE DECIDED THAT A STERILE COCKPIT WAS GOING TO BE NECESSARY WHILE ON THE GND; IN THE CLASS D AIRSPACE AND BELOW 2000 FT AGL. ONLY QUESTIONS RELATED TO THAT PHASE OF FLT WOULD BE ALLOWED. SHE WILL NOW HAVE A NOTE PAD TO WRITE DOWN QUESTIONS TO BE ANSWERED LATER. I AM NOW MORE VIGILANT WHILE ON THE GND AND I WAIT UNTIL CLRNC TO RECEIVED BEFORE PERFORMING THE LINE-UP CHKLIST TO PREVENT THIS FROM HAPPENING AGAIN.