<P> O - levels were predominantly exam - based; this had advantages for students in part - time or evening education . Some commentators criticised this mainly exam - based approach as offering only partial proof of the student's overall ability in comparison with other methods (e.g., coursework - based assessment). There was no summative "school certificate": each subject was a separate O - level in its own right . </P> <P> Madsen Pirie found that the O - level was advantageous to boys because of exam - based learning . Pirie also observes that the GCSE focus on coursework has disadvantaged boys, reversing the gender gap in attainment, to the degree where in all subjects girls outperform boys, including traditionally male subjects such as sciences and physical education . </P> <P> Initially candidates were only awarded a pass or fail classification, though the independent exam boards soon offered competing numeric and alphabetic classifications, for example 1, 2, 3, 4, 5 and 6 would be a pass, while grades 7, 8 and 9 were fails from the JMB . From 1975 standardized alphabetic grades where introduced with grades A, B, C, D, and E were passes, and f and U (Unclassified) were fails . Between 1965 and 1985 grades were allocated primarily on a norm - referenced basis, assigning a fixed proportion of each cohort to each grade (A 10%, B 15%, C 25 - 30%, D 5 - 10%, E 5 - 10%, U 15 - 20%). Though some exceptions existed, both at the subject and Exam Board level, with Latin and Greek pass rates being consistently higher than other subjects, with 75.4% passing in 1976, in contrast to an average 59% pass rate across all subjects e.g. Biology 56.4%, History 57% . The pass rate and top awards by the Oxford & Cambridge board were also consistently higher than the other boards e.g. In 1976, 27% of Latin entrants gained an A, and ~ 17% of French, German and Music candidates, this was attributed to the O&C board being primarily used by the Independent schools . The proportion obtaining a pass, A-D, or equivalent was initially fixed at 57% - 58%, and remained under 60% through the 1970s, though there was regional variation with Northern Ireland awarding consistently more pass grades than Wales e.g. In 1982, the pass rates were: Northern Ireland 62%, England 58% Wales 53% . In 1984 a decision was taken, by the Secondary Examinations Council, to replace the norm referencing with criteria referencing, where 16 + and 18 + grades would in future be awarded on Examiner Judgement, this change was implemented, at O - Level, in June 1986 . In the final year DES statistics were available 6.8% achieved an A, and 39.8% an A-C grade . </P> <P> O - levels incorporate an element of negative marking, with marks deducted for incorrect answers, poor spelling, grammar or handwriting . </P>

When did o level grades change from numbers to letters