Following a period of instruction in stalls and steep turns, the student pilot returned to the aerodrome for practice in crosswind landings. Several dual circuits and landings were carried out, and the student was authorised for solo practice. The wind was about 10 knots, and gusty. The pilot completed six circuits without experiencing any problems, making a touch and go landing each time. As the aircraft was rolling along the runway just prior to the pilot retracting the flaps and applying power for his next circuit, the aircraft was struck by a gust of wind which lifted the right wing. The aircraft then veered sharply to the right, and the pilot was unable to regain control. The aircraft came to rest in a shallow drainage ditch. The student was possibly feeling the effects of fatigue. He stated that after the touch down he had returned the ailerons to the neutral position, having forgotten to maintain aileron control into wind to counteract the gusty crosswind effect.