The student pilot satisfactorily completed two normal circuits and landings and one short field landing in calm, clear conditions. He made an approach for a second short field landing but as the aircraft neared the aerodrome boundary fence on short final, the stall warning sounded. The pilot states that he applied power, but the port wing dropped sharply and struck a fence post 107 feet to the left of the runway centre line and just short of the threshold. The aircraft pitched forward onto its nosewheel and propeller, tearing off the yoke and nosewheel and then the starboard undercarriage strut and mainwheel as it rolled in that direction. It slewed on the starboard mainplane in an anti-clockwise direction before it came to a stop on a reciprocal heading.