On May 6, 2004, at 1200 eastern daylight time, a Cessna 152, N94577, was substantially damaged during landing at the Pottstown Limerick Airport (PTW), Pottstown, Pennsylvania. The certified flight instructor and student pilot were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the instructional flight conducted under 14 CFR Part 91. According to the flight instructor, the purpose of the flight was to practice landings with the student pilot. During the landing flare, the student pilot noticed he was slightly left of centerline and applied full right rudder to correct. The nose of the airplane then turned sharply to the right, and the flight instructor applied left rudder to straighten it. However, the airplane had already drifted to the left side of the runway, touched down on the edge of the pavement, and the left wing impacted a tractor that was cutting the grass on the side of the runway.