My 8 year old DS has very good reading comprehension. He reads books for pleasure in addition to assigned books from school and he is recently reading books of the level of "The mysterious Benedict society". When questioned, he can go on and on about the detailed plots and twists in these books and seems to have a good grip on the story lines and seems to use his knowledge and real life experiences to tie them to the story lines and make inferences. He also scores an A+ or A on his literature classes in school (he is grade skipped and the content is fiction, classics, biographies) and very highly in the comprehension part of the annual standardized testing.
But, when he is reading non-fiction (for e.g. a science textbook that is above his age level), he seems to lose focus and is unable to get the underlying concepts correctly and he is missing out on smaller details or cannot retain them in his memory. Are there any ways to help a motivated child improve his comprehension for non-fiction work? He wants to study a lot of astronomy and biology in the upcoming year and is disappointed that he cannot follow the books on these topics that he picked out from the library.