All three of my sisters kids (now 11, 13 and 16) have been tested for learning disabilities, ADD/ADHD - they've even considered in enrolling in a study through Georgetown university regarding heredity of learning disabilities as their father has dyslexia.
Last Christmas, my nephew was 9, and we were playing the game Apples to Apples. It was very difficult to watch him struggle with simple words. He attends a good school in one of the most acclaimed public school systems in the country, and they keep advancing him from grade to grade because he's not "non-proficient" enough to be held back.
There are certainly emotional/psychological things to take into consideration - what needs to receive equal merit, though, is what effect his struggles in the current and subsequent grades will have as well.
I, too, believe McMama makes some good points that warrant consideration and are completely valid.
More than anything, I'd ask your son how he feels about things and what he'd like to do and then support him fully with either your own time and investment into helping him in each grade, getting a tutor with whom he really clicks.
My brother in law was coddled and told it wasn't his fault. As a 41 year old man, he writes like an 8 year-old and won't work for anyone other than himself for being exposed for his disability. His parents completed school work for him to help him pass and completely enabled him NOT to learn and to learn how to overcome this issue.
Good luck! I hope you make the right decision and find your son thriving in years to come.