According to the flight instructor, the flight departed to conduct airwork and grass field landings. The pilot under instruction was seated in the rear seat, and the flight instructor was seated in the front seat. The pilot under instruction stated that the flight instructor was on the flight controls at the same time since it was going to be his first landing on a grass strip. However, the flight instructor stated that he advised the pilot under instruction, “you have the controls,” and received acknowledgement. On the first touchdown to runway 28, the tailwheel-equipped airplane bounced and became airborne, then touched down a second time. After the second touchdown, when the airplane began turning to the right, the flight instructor “got on the controls” and added left rudder, which was “ineffective.” The airplane then ground-looped 90 degrees and struck a clump of spruce trees. Post-accident examination revealed that the airplane incurred damage to both lower wings. Neither pilot reported any preexisting mechanical malfunctions or anomalies with the airplane, and winds were reported as being from 200 degrees true at 7 knots.