STUDENT PLT IN C172 DURING A SUPERVISED SOLO FLT BECAME CONFUSED WITH TWR INSTRUCTIONS WHEN TWR MADE RWY CHANGE. HOWEVER; TWR STAYED WITH HER AND ASSISTED HER TO THE PROPER DOWNWIND LEG AND RWY FOR LNDG.

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I SENT A STUDENT SOLO IN THE PATTERN AFTER COMPLETING A SHORT FLT IN THE PATTERN WITH HER. COS WAS LNDG RWY 35L/R AND RWY 30 AT THE BEGINNING OF THE SOLO FLT; AND I WAS MONITORING ON THE GND. DURING THE SOLO FLT; COS CHANGED RWY 17L/R AND RWY 12. TWR INSTRUCTED MY STUDENT TO TURN R AND FLY NBOUND AND TO EXPECT RWY 17R. (SHE WAS ON DOWNWIND FOR RWY 35L AT THE TIME.) SHE MADE THE R TURN AND HEADED NBOUND. TWR EXTENDED HER DOWNWIND AND I LOST SIGHT OF HER AT THAT POINT. APPARENTLY SHE ALSO LOST SIGHT OF THE RWY. WHEN TWR FINALLY CALLED HER BASE; SHE WAS A GOOD DISTANCE FROM THE RWY AND WAS UNSURE OF HER POS. TWR ASKED IF SHE HAD THE RWY IN SIGHT; TOLD HER AGAIN TO TURN BASE FOR RWY 17R. MY STUDENT BELIEVED SHE SAW THE RWY; BUT WAS ACTUALLY LINED UP FOR RWY 12. AT THIS TIME THE TWR ASKED AGAIN IF SHE WAS SURE SHE HAD RWY IN SIGHT AND TOLD HER IT WAS 'THE ONE RIGHT IN FRONT OF YOU;' WHICH ADDED TO HER CONFUSION. ANOTHER FACTOR CONTRIBUTING TO HER CONFUSION WAS THE FACT THAT WHEN SHE SET HER HDG INDICATOR AT TKOF; THE KNOB STUCK IN AND THE HDG INDICATOR WAS NOT INDICATING CORRECTLY. WHEN SHE APCHED RWY 12 SHE REALIZED SHE'D GONE FOR THE WRONG RWY AND INITIATED A GAR; BUT SHE CONTINUED ON RWY 12 HDG; WHICH PUT HER ON A COURSE FOR THE PATTERN OF THE PARALLEL RWY (RWY 17L). TWR TURNED HER SBOUND AND THEN W TO REJOIN THE DOWNWIND FOR RWY 17R. THERE HAD BEEN TFC IN THE PATTERN FOR RWY 17L WHEN MY STUDENT DID HER GAR; AND SHE SAW IT; TRIED TO TURN AWAY; BUT UNFORTUNATELY TRIED TO TURN NBOUND. THAT'S WHEN TWR TURNED HER SBOUND. NO NMAC OCCURRED AND THE FLT WAS ROUTINE AFTER THIS. I THINK CONTRIBUTING FACTORS TO THIS INCIDENT WERE MY STUDENT'S FAILURE TO ASSURE THAT THE HDG INDICATOR WAS FUNCTIONING PROPERLY AFTER TKOF; THE TWR CTLR'S CONFUSING INSTRUCTION (IT'S THE ONE RIGHT IN FRONT OF YOU' WOULD HAVE BEEN BETTER UNDERSTOOD AS 'IT'S THE SBOUND RWY'). I WILL MAKE EXTRA SURE THAT MY STUDENTS ARE ABLE TO LOCATE L AND R TFC PATTERNS FOR ANY RWY FROM EXTENDED DOWNWINDS IN THE FUTURE.