Do not worry, some children read slower than others. You can help your son by guiding him starting from the basics. Then each week, he will begin to progress and will read better. I hope this can help your situation, good luck and have a great week!
I suggest finding a good fluency passage book and practicing it with him. You read one sentence with normal speed, accuracy, and expression, snap your finger, and have him read the exact same sentence, with the same speed, accuracy, and expression as you. (If he stumbles, try chunking the sentence into normal phrasing breaks, about 3-4 words that naturally go together, then snap and have him repeat.) It IS ok if he seems to echo you, just make him drag his finger along the words as he reads so that he gets in the practice of connecting the words with the fluent way to read. And do this through the entire passage. The passages should be fairly short. Start with a lower than his reading level fluency practice book, so that he has success. You could even use easy reader book you already have. Scholastic has some, but I also bought intervention guides that were a part of teacher editions of textbooks, that are no longer being used, but are still excellent resources. Biblio.com sells all sorts of used teacher editions. I bought Macmillan/MacGraw-Hill Reading Fluency Assessment Grades 1-3 and Grades 4-6. Fluency is the key to reading like good readers should. Time (1 minute) and score the first attempt at reading the passage all alone. Practice it everyday, then test him again after a week. You WILL see growth and a boost of self confidence, as well. Also, as you listen to him read, you will pick up on areas such as phonic strategies and such where there are gaps, and you can go back and work on those with him. Education.com has fantastic phonics worksheets and fun activities. Good luck and have faith!
There may be several reasons for this. Consider the following: is he dyslexic? Does he have visual problems? Once you have eliminated these, then begin at the basics when learning to read. Start with logo read - does he recognize McDonald's, Walmart, KFC signs? Yes - then move to pictures - does he recognize the pictures? Then give him the first letter of each picture - c = cat, d = dog etc.
Education.com has wonderful phonics, reading and writing worksheets as they start at kindergarten level. Use these as they include the writing of these letters as well. Work through their program everyday teaching him 3 letters at a time.
I wish both you and your son well. One step at a time and you will see the progress.