INSTRUCTOR; WITH FIRST TIME STUDENT; TAXIES INTO LADDER USED TO CHK FUEL.

Narrative

THIS INCIDENT INVOLVED A C172 AND A 2 STEP; COLLAPSIBLE LADDER. A YOUNG MAN; ON HIS FIRST FLT; WAS WITH ME. I'M EXPLAINING THE PREFLT; TO HIM; AND HE WAS ASKING MANY QUESTIONS. I CHKED THE FUEL IN THE L WING; USING THE LADDER TO GET TO THE FUEL CAP; TOOK THE LADDER AROUND TO THE R WING AND HAD HIM CHK THE FUEL IN THAT TANK; INSTRUCTING HIM TO MAKE SURE THE FUEL CAP WAS SECURE. I CONTINUED THE PREFLT; NOT PERSONALLY ASSURING THAT THE LADDER HAD BEEN REMOVED. HE MUST HAVE MOVED IT FORWARD OF THE R WING AND TO THE R; I DID NOT SEE IT. WE STRAPPED IN; COMPLETED THE CHKLIST; STARTED THE ENG; RECEIVED TAXI CLRNC; PULLED OUT AND TO THE R WHEN CONTACT WAS MAE. MY INITIAL THOUGHT WAS THAT THE R MAIN GEAR HAD CONTACTED SOMETHING. I STOPPED; SHUT DOWN THE ENG; GOT OUT AND DISCOVERED THE LADDER PIECES; ON THE RAMP. I REMOVED THEM; INSPECTED THE R MAIN GEAR AND THE PROP AND DETERMINED THE ACFT SAFE TO FLY. THE FAA MET US ON OUR RETURN; 1 HR LATER. MORAL: MAKE ABSOLUTELY CERTAIN AREA IS CLR OF EVERYTHING; BEFORE STARTING THE ENG AND TAXIING.