The flight instructor told the pilot he wanted to demonstrate adverse yaw during the landing. The flight instructor maintained control of the ailerons and the pilot maintained control of the rudder. The flight instructor put in left aileron during the landing roll out, resulting in the airplane to drift to the right. The pilot put in left rudder and the airplane continued drifting right, turning about 90 degrees from the runway heading. During the turn to the right the left wingtip dragged on the ground, substantially damaging the left wing.