I'm trying to help improve my 13 yo :confused: son's reading comprehension but don't know how, he is already and avid reader with a great vocabublary. What else can I do to help him

Have him write an outline on what is the main point of the story with an outline of the stories main points and below list major/minor details.
Then go over it with him and help him understand that maybe while what he put as a main point such and such might be a better point. Then go over the outline and help him see why something should be in another category.