The certified flight instructor and the student pilot flew to a practice area to work on hovering techniques. Before the flight instructor turned over the controls to the student, he discussed with the student how to make a positive transfer of the controls and also the importance of not having a tight grip on the controls. The student took control of the helicopter and practiced hovering for approximately 10 minutes, when the flight instructor felt the helicopter begin to settle. Before the flight instructor could react, the student pilot "quickly" pulled the collective full up, which overrode the throttle and the main rotor began to lose rpm. The instructor immediately made an attempt to lower the collective and increase engine rpm, but the left skid contacted the ground, and the helicopter rolled over on to its left side. The helicopter sustained damage to the main rotor blades and the firewall.