Automaticity in decoding is needed to read fluently, and reading fluently is required for comprehension. Working memory is the “table space” your brain has to manipulate information in your head. Some people have more “table space” than others to manipulate information and to make meaningful connections in the text they are reading with their prior knowledge and experience. Those with smaller spaces can only hold on to little bits of information while the rest “falls off the table”. But if you do not have automaticity in decoding, most of your table space will be taken up by decoding, so you will have less space to retain the information that you are reading and this then leads to comprehension problems.
Imagine if you are learning a foreign language and you are reading something in that language – imagine the effort it takes to read and simulataneously translate the words in your head as you are reading. You are spending so much time translating each word that by the time you get done reading, you really didn’t retain what you just read because you spent most of the time translating words. This is the type of effort and what happens when a person that does not have automaticity in decoding experiences when reading. So if someone says your child has a “disability in reading comprehension”, you may want to dig deeper to see if the problem really stems from a disability in decoding.
Rapid Automatized Naming (RAN) and Reading Fluency: Implications for Understanding and Treatment of Reading Disabilities by Elizabeth S. Norton and Maryanne Wolf