During the floatplane instructional flight, the private pilot decided to make a practice landing and takeoff on a large lake. Although the landing on the calm water was uneventful, during the takeoff run, just before liftoff, the aircraft encountered the wake of a large boat. As the aircraft crossed the crest of the first wave of the wake, it became momentarily airborne, and then it impacted the advancing forward face of the second wave. At the moment of impact, four of the float attach fittings failed. The pilot therefore immediately aborted the takeoff, but the right wing impacted the surface of the water before the aircraft came to a stop. Neither the private pilot nor the instructor pilot that was supervising him had seen the large swell approaching during the landing, and during the takeoff run, neither of them noticed it until a few seconds prior to the time the aircraft impacted it.