The flight instructor, who was seated in the front seat, and pilot receiving instruction practiced three landings on the hard surface runway in the tailwheel-equipped airplane. The flight instructor reported that he then asked the pilot to conduct a 3-point landing on the grass adjacent to the runway. The instructor reported that the pilot got high and slow on short final and that he told the pilot to lower the nose and add power. He stated, “[pilot] was slow to respond [and] pulled the nose up (stick fully aft) for the landing.” The instructor stated he was too late to add power, and the airplane stalled about 5 to 8 ft above the grass. The main landing gear collapsed, and the airplane nosed over. The instructor reported that there were no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation. The pilot receiving instruction reported that while over the grass parallel to the runway threshold, he began to flare the airplane. The instructor stated the flare was initiated too high but to continue the landing. The airplane leveled out, and the instructor stated to “keep pulling.” The pilot reported the instructor began to manipulate the controls with the pilot, and the instructor pulled back on the control stick. The airplane entered an extreme nose-high attitude, stalled, and impacted the terrain. The pilot reported that there were no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation. The airplane sustained substantial damage to the vertical stabilizer and rudder.