knitting I do remember feeling like that in my first English Literature A level, I could not understand how to analyse. The second time I took it I understood; it was a trick PEE based on thorough understanding of themes and then things like structure and context, also through pointing to techniques like symbolism, rhetoric, contrast, imagery, tone, texture, irony, satire, narrative voice. Very much like analysing music I would think...you just have to break it down and you start to see patterns developing when at the beginning all you can hear is nice noise and nasty noise...
I would say off the top of my head that most non-fiction tells a story and there are series of "tricks" to make that story unfold successfully and keep you listening.
But as you can probably tell, I don't know the exact syllabus of English Language A level 
Did your son know that the Sun is famous for its alliteration? 
My aunt once did a thesis on hyphenated and non-hyphenated word use..
I once tried to explain to Ds1 why Big Fish was such a clever film (the one with Albert Finney) because of the title pun, and he never understood...they just do have this basic incomprehension. I also tried to explain to dd recently about Much Ado About Nothing being a pun on Noting, and she again was ...who cares...