THE STUDENT & INSTRUCTOR (CFI) ELECTED TO VISIT AN ARPT WITH A NARROW RWY WHERE SMALL ACFT WERE BUILT & FLOWN. THE 1ST APCH WAS NOT TO THE CFI'S SATISFACTION, SO A GO-AROUND WAS MADE. THE 2ND APCH WAS GOOD, BUT DRG THE LNDG, THE STUDENT 'FROZE' AT THE CONTROLS & THE CFI WAS UNABLE TO RELEASE THE STUDENT'S GRASP. SUBSEQUENTLY, THE ACFT BOUNCED, THEN IT WENT INTO A BORDERING CORN FIELD & WAS DAMAGED. THE CFI SAID HE REPEATEDLY TOLD THE STUDENT TO 'LET GO,' BUT THE STUDENT CONTINUED TO STAY ON THE CONTROLS.