Blessed Mommy, so glad that youhave figured this out early and that you have such a supportive school environment. I think that you are way ahead of the game already.
FWIW, we figured out that our DD, who is now 13, is a gifted dyslexic when she was about your son's age. She tested into our district's gt program in lst grade but struggled with the spelling and writing requirements. We watched her self-esteem take a nose dive and thought about pulling her out of the gt program. We took her for private testing between 1st and 2nd grade. The testing showed that she was HG with dyslexia and dysgraphia. After that, I started to read everything in sight on dyslexia in gifted children.
I agree with polar bear that there seem to be varying definitions of dyslexia that may be confusing, we chose to tell DD and use the stealth dyslexia terminology from the Eides. For us, it helped to explain why she might not look like what other people call dyslexic. We also chose to use the term because her dad identifies himself as a dyslexic as well.
For DD, we were trying to help her develop an alternative narrative - one where you could be smart even if you weren't the world's best speller. She already knew that she struggled more with writing and spelling than her siblings and classmates. We tried to help her understand that her brain is wired differently. We showed her some of the images from Sally Shaywitz's Overcoming Dyslexia. DD found the fMRI brain images fascinating.
For us, the decision about how much to tell DD has evolved over time. I've never showed her the test results. At the same time, one day when she was sobbing about she was so stupid and would fail grade school, I reassured her that she is intelligent. I told her that her testing showed that while she struggled in some areas, there were other areas where she scored extremely high. I told her that if a 1000 kids took the same test, she would score better than all 999 other kids. I needed to give her some outside reassurance that something/someone other than mom thought she had potential and ability. We also talked about how some things that are easy for other kids would be hard for her (i.e writing and spelling). I also told her that once she got past learning some of these basics, things that were hard for others would be easier for her. Now that we are in middle school, she is seeing this but is has been a long road.