The flight instructor in the tailwheel-equipped airplane reported that, while the pilot receiving instruction performed a wheel landing, the touchdown was smooth and normal. The pilot reduced the power to idle, the tailwheel lowered, and the airspeed decelerated to about 30 knots. The airplane turned slightly to the right and the pilot corrected with "slightly too much left rudder", followed by "too much right rudder", which led to a ground loop to the right. The instructor attempted to recover with heavy left rudder and decided to perform a go around. He attempted to add power, but was unable to advance the power lever, which he believes was being firmly held by the pilot. The left wing impacted the runway and airplane tipped onto its nose, The airplane sustained substantial damage to the left wing. The flight instructor reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The airport's automated weather observation station reported that, about 4 minutes before the accident, the wind was from 330° at 7 knots. The pilot landed the airplane on runway 12.