Prior to 1963 OCSEB used scaled marks ranging from 0 to 90 in grading O Level results. The highest grade was 90 and 45 was the lowest grade of pass. In 1963, in common with many examination boards, they adopted a number grade of 1 to 9 (1 being highest and 6 being the lowest grade of pass). Although schools were given access to this unofficial number grade, the grades were not recorded on the certificates awarded to candidates: O Level results were expressed officially as pass or fail only. The GCE examination boards felt this was unjust to candidates who had just failed to obtain a pass and thus had nothing to show for their efforts, and made recommendations to the Schools Council for O Level grades to be made official, i.e. recorded on certificates, as was already the case with CSE examinations.

A proposal to adopt five official grades at O Level was approved by the Schools Council in July 1973 and the grades A-E were introduced in 1975 with the former O Level pass/fail mark being equated with the C-D borderline.

In Spring 1975 a series of Agreement Trials were carried out amongst the GCE examinations boards to agree criteria for Grades D and E and for the Unclassified category. Each board supplied the scripts of twelve candidates who sat examinations in Summer 1974, with marks ranging from just below Grade 6 to just below Grade 8. Each Board reported their opinion as to where the D/E and E/U borderlines should be in all of the scripts.