During the transition from a hover to a landing, the student pilot began to lose directional control of the helicopter. The certified flight instructor then attempted to take control of the helicopter, but he did not ensure that the student had completely removed his feet from the anti-torque pedals. Since the student's right foot was still in contact with the right anti-torque pedal, the aircraft spun to the right approximately two full rotations before impacting the ground and rolling onto its side.