There have also been concerns about ADD, and the child needing repeated reminders (especially, for fine motor skills tasks like writing). We'll definitely consult a psychologist and see what they say/think as well..
I'd suggest a neuropsych eval based on what you wrote here and in your intro thread. The reasons I'd choose a neuropsych over a regular psych are:
1) The school is concerned about ADHD - and if you can get private data now showing ADHD or not - that will help you by either leading you in the direction you need to go to help your ds where he needs help, or will give you the report to back you up when ADHD is suggested again and shut down that conversation quickly.
2) You've got achievement testing now but still don't have ability testing - that will be part of a neuropsych eval, and it will most likely be helpful in advocating for gifted services if you decide at some point to transfer to a different school. JMO, but I think the ability testing would be helpful to you in the situation you're in at now with your ds' school - your previous intro post was titled something like "gifted or pushed" and you'd mentioned the school seemed to think you were pushing your ds. Having an actual IQ score will help you counter that type of reasoning.
3) The neuropsych, if they are local to you, may have valuable insight re which local schools would work well for your ds.
4) While I agree with the previous poster who mentioned getting thoughts into writing can lag behind other academic skills, particularly at this age, I'd still want a little more clarity on why the writing is lagging. You have one tester's observations and opinions. Does it match what you see? Have you had any measure of your ds' handwriting speed relative to same-age peers? Is he doing ok with punctuation, not reversing letters, etc? Is his handwriting relatively neat and legible or is it all over the place? Has he learned how to tie his shoes yet? How is he doing in school when given a writing or story telling task? How is he doing when given a fine motor task? A neuropsych will be able to tell you if there is something to be concerned about. Chances are there isn't, but otoh, if there is - it's better to catch it earlier than to have it be an issue that holds him back from accelerated placement.
I'm also wondering - has the school staff mentioned anything else other than fine motor and having to prompt him to keep him on task as reasons they suspect ADHD? What's your gut feeling re ADHD - do you see signs of it at home or in other situations?
Best wishes,
polarbear