I never heard of a lower pass mark being set explicitly for boys of less ability butI I know that some of the teachers tried to be more generous when marking the papers of boys who had less aptitude for the subject in question. I was told that a few years later by one of my old teachers whom I got to know quite well because we both went to the same pub. He also told me that he (and some of his colleagues) used to skim through a selection of exam papers before he started to mark them and tried to assess how severe or how lenient he could afford to be.