During the takeoff roll in a tailwheel-equipped airplane, the private pilot pushed the control yoke forward to lift the tail off the ground. When the tail came up, he lost control and the airplane ground-looped. The flight instructor, who was checking the pilot out in the airplane, tried to regain directional control, but the airplane went off the runway and flipped over causing substantial damage to the airframe. No mechanical issues were reported prior to the loss of control.