This is no official secret - just the opposite in fact - but 'comprehension' is defined for us by the publishers of those handy study guides, CGP. All the questions on the rehearsal Key Stage 2 SATs Comprehension test come under the following headings: Retrieval, Inference, Summary, Lay-out and Structure.
So, Retrieval is that one where the passage says, 'Bob had a blue hat' and the question is 'What colour is Bob's hat?' Inference is where the passage says, 'It was raining. Bob had a blue hat.' and the question is, 'Why was Bob wearing a hat?'. Summary is of course summarise 'It was raining. Bob had a blue hat.' (!). Lay-out is where they ask you questions about, say, punctuation, or eg why the passage also had two boxes of information next to it, or some such. And Structure is where they ask you about why this or that came before or after this or that or the like.
So that's comprehension done and dusted.
Or is it? What's missing? Well, only all the stuff that you really engage with, all the stuff that is the reason why you would ever read anything, talk about it, wonder about it, be affected by it, care about it. That's to say the mix of ideas and feeling which all writing bar the most scientific, most instructional, deals with. All the writing that is put in front of KS2 SATs students will have lying behind it and threaded through it a set of ideas. The chances are these won't be simple or clear-cut and can't be easily reduced to yes/no answers and so are 'difficult to mark'. Likewise, the feelings that might be engendered by a reader reading the passage.
Ah well, the defenders of the retrieval/inference/summary/lay-out/structure school say, you can't get the ideas from a passage unless you do retrieval, inference,summary,lay-out and structure. To which I say, yes but... My yes-but is this: do you approach the matter of comprehending a piece of writing with that list of testable activities or do you approach it through a discussion of its ideas and the kinds of feelings you perceive to be present in the text and/or in yourself? I would argue that by engaging with ideas and feeling, particularly in close reading of a text and in discussion with others, the questions of retrieval, inference, summary, lay-out and structure emerge.
The sad story, though, is that some schools under pressure to perform in the SATs feel that they have to drill on retrieval, inference,summary,lay-out and structure rather than spend time in a much more discursive way talking about ideas and feeling as a route to those SATs-type 'skills'.
Similarly, in the run-up to the SATs a good deal of other kinds of work which really engage with ideas and feeling in stories, non-fiction writing, poetry and the rest also slip off the time-table - drama, performance, interpretation-work eg doing art- and music-work inspired by a piece of writing.
It's hard not to feel suspicious about all this. That's to say, in many schools, trying to do their best to stay out of trouble with Ofsted, children are being steered away from time spent engaging with ideas and feelings and spending time instead getting the retrieval, inference,summary, lay-out and structure stuff 'right'. Conspiracy theory tells me that this suits the present era nicely - preventing children from thinking, discussing, arguing for and against ideas and feelings emerging and lying behind texts and urging them to thinking that all writing has right and wrong answers to fixed questions.