ON FINAL APCH AFTER A TRNG FLT, AN ACFT WAS STILL ON THE RWY, SO CFI TOLD 30 HR STUDENT PLT TO GO-ARND. POWER WAS APPLIED & WITNESSES ON GRND HEARD ENG REV UP OK. ABOUT 1/2 WAY DOWN RWY AT ABOUT 200 FT, THE ENG SPUTTERED & CFI TRIED A 180 DEG TURN BACK TO RWY. ACFT HIT FENCES AND CONST MATERIAL & BURST INTO FLAMES. FUEL SEL WAS FOUND OUT OF DETENT BUT ON LT TANK WHICH HOLDS 30 GALS, 26 GALS USABLE. THE ACFT BURNS ABOUT 8 GPH & HAD FLOWN FOR A TOTAL OF ABOUT 4 HRS SINCE TOPPED OFF TO 60 GALS CAPACITY. NO FUEL FOUND IN FUEL MANIFOLD & ENG WAS TEST RUN OK AFTER ACCIDENT. LT WING TANK AREA HAD LESS FIRE DAMAGE THAN RT WING AREA WHICH CONTAINED MORE FUEL. THE STU PLT RECALLED THE FUEL SEL BEING ON THE LT TANK; THE CFI SAID HE THOUGHT IT WAS ON THE RT TANK. THE CFI STATED THAT HE HAD NO RECOLLECTION AFTER THE ENG QUIT EXCEPT BEING IN A CHOPPER ON THE WAY TO A HOSPITAL.