Apprentices still faced some form of examination before they finished their time. In those office jobs, examinations were often the avenue that delivered advancement.
Remain at school for another two years, and your subject load dropped from eight to six, while the knowledge requirement ratcheted up and you continued to hone your examination question answering skills.
When you sat for Senior, the carrot was a place at University while the consolation prizes, if you failed to matriculate or couldn't afford to head off to University, included Teachers' College and the Commonwealth public service, and essay writing remained on the horizon.
University, however, added another element to the essay-writing equation.
Up to this point, you were demonstrating that you had a grasp of your subject. History wasn't just a string of dates and events, causes and effects, but all you seemed to need to do was demonstrate that you knew the sequence of events that led up to here and the way people and events contributed to a particular outcome. Explanations were best given in terms of the conventional wisdom.
Or, at least, that was the way things worked in Year Ten. My six Senior subjects did not include History. (1)
University level History introduced three new elements to the essay writing equation.