Comprehension is putting it all together. If a person has difficulty with any of the other areas of reading (Phonological Processing, Decoding, Fluency and Vocabulary) then they will struggle with reading comprehension. Reading with understanding will take a very, very long time, taking two or three times longer than it should. If a person is “reading” words fluently, even at grade level, but they don’t understand what they just read then they are just "word calling" which is when they identify the individual words without making the necessary connections to create meaning.
Fluent or not, the absolutely most critical key for developing excellent reading comprehension is…. QUESTION ASKING!
A good reader asks themselves questions all of the time…so fast that they don’t even realize that they are doing it any more! A student who struggles with reading comprehension needs to learn how to ask questions: at the word level (vocabulary), the sentence level, the paragraph level, and ultimately longer passages. Asking questions will help them to see the relationships, understand the inferences, and draw conclusions.
The key is to make sure your reader is interacting with the material - thinking their way through it vs. word calling!