The flight instructor and student reported that they were practicing touch-and-go takeoffs and landings, and during the second approach, the airplane's airspeed and altitude decreased further than intended. Subsequently, the left wing contacted the runway resulting in substantial damage to the left wing tip. The flight instructor took control and landed the airplane. While taxiing to the ramp, they observed that the winds had increased more than reported. The winds recorded at the airport, prior to and after the accident, were variable from the west and south at 7 to 10 knots, and gusting up to 17 knots. The flight instructor reported that there were no mechanical failures or malfunctions of the airplane.