The certified flight instructor and his student were performing a soft field take off. He reported that while in ground effect after liftoff the student was not applying sufficient right rudder to offset wind drift and the left turning tendency of the airplane due to P-factor and torque. As the airplane drifted to the left side of the runway, the flight instructor physically took over the flight controls. The flight instructor commented that he dropped the nose of the airplane to attain flying speed and inadvertently touched down on the left side of the runway. He then proceeded to takeoff and fly the lesson with the student. After returning to the airport at completion of the flight lesson, a visual inspection found that the right wing tip and aileron sustained substantial damage. According to an eyewitness, the right wing of the airplane appeared to have struck the ground when the airplane touched down. The pilots reported no mechanical malfunctions or failures that would have precluded normal flight.