Marlborough College, in Wiltshire, had 17 pupils upgraded after complaining about the marking of the 1997 exam.
Headmaster Edward Gould said: "It was immediately obvious to us that the 1997 results were random."
The Southern Examining Group re-marked all 144 scripts and 11 were upgraded. But the school was still unhappy and appealed to the independent exam ombudsman. The ombudsman judged there had been no national problem with the exam and that the mark scheme had been correctly applied. But the Independent Appeals Authority for School Examinations was not satisfied with SEG's re-marking.