Well, in our DS's case, he really does whip through books quickly. I am a super fast reader (I still remember being accused by a public librarian of cheating during a summer reading program when I was a child because she didn't believe that I could have read "that much in just a week" and am thus super sensitive to this issue), but even I wonder about my DS. This is in part because I know DS tends to skip around when he is reading, and often reads the ends of books first, so I sometimes am not sure he has actually gone back and read the beginning.
I am not 100% sure what is meant by comprehension in this context either - does it mean understanding the story, or understanding the vocabulary? My DS often understands what he is reading, but there are often vocabulary words he doesn't get (he has been reading non-fiction about the American Revolution). We work hard to teach him to ask about words he doesn't know, but the reality is, when he is in the middle of something, he doesn't really want to stop and find us to ask or look up the word in the dictionary.
