I never heard of the discrimination against girls with regard to the lowest passes. I went to a Girls' Grammar, but there was also a Boys' Grammar, two mixed Grammars, a boys' and a girls' Catholic Grammar two bi-lateral schools and in 1957 the first Comprehensive school to open. There was a range of secondary schools, some very good and forward thinking, and just one dreadful one, which had endless resources poured into it to improve it, but an endless struggle.
I was told that boys suddenly discovered they had brains at about ten; the kindly secondary school master was spinning something of a yarn about boys developing brains in their teens; more to do with social conditioning: boys were expected to have careers, girls to have jobs before they got married.
The girls' grammars generally promoted the idea that women could do anything, and were expected to do so, definitely a career and appropriate qualifications, degrees, teacher training, medical, engineering, art, drama, secretarial qualifications of all types.
Women's Lib without all the shouting.