At the conclusion of a dual check flight, the student landed the aircraft into a light north-westerly wind. The landing roll was completed about half way along the 853 metre strip, and the pilot turned the aircraft around preparatory to taxying back to the upwind threshold. The instructor left the aircraft at this point, after briefing the student on the solo sequences he wished him to practice. Shortly afterwards, full power was applied as the student commenced a take-off downwind. The aircraft failed to become airborne, collided with a fence and overturned. The student was subsequently unable to give any reason for his decision to commence the take-off roll from other than the threshold of the strip.