What does your son see as the problem? Does he even see a problem? Is he frustrated, disinterested? Taking responsibility for hard work? Does he want to know why he has writing problems? Has he always had writing issues? If it were me, I'd want a clearer understanding of what the teachers see, and what your son does so that I could investigate on my own.
He just says that he has nothing to say. He does see a problem but he doesn't know what to do. Up till about 4th grade he was well above average at writing. First sign of a problem was the first essay about "tell me about yourself" in the GT class in 4th grade he wrote 1 1/2 sentences. But it got better that year. He has problem in 6th but we didn't really address the writing problem, instead worked on his social/emotional problems. Things seemed to be better by 8th grade last year.
So he wants it all in his head before he starts writing. Well, lots of kids want that. Is this a sign of a disability or does he have flexibility about this? I know my kid can get really stubborn about what he will and won't do and it has not much to do with his disability. So, I'd want to try to flesh out what is disability related and what is boredom, and what is "I can't do this over and over and over again. It's just too hard".
It's hard to figure out if there is a disability, or if this is just boredom, or stubbornness. It may be a bit of all three? I think once he gets frustrated about an assignments, it's impossible to get him back on track. It's clear that the poetry he is supposed to write about now he has zero interest in. This is partly why I haven't pursued any of these avenues before now. He was struggling with writing to prompt early this year, but he could usually figure out what to say even if he didn't have time to finish the essay. I haven't seen him this stuck since 6th grade.
This is why I want him to work with the educational therapist. She will work on writing strategies with him one on one.
I don't know if you feel the same, but that's my approach. We have a 504 meeting coming up and I'm full into detective mode so I can figure out what's going on and what accommodations are needed.
Be prepared for the team to tell you there's nothing wrong. He's normal,leave him alone and don't push him into honors classes. If you have specific items to relate that are clearly "abnormal" that will help.
Also be prepared to ask for whatever testing you might need. I'd ask for testing regarding written expression--Test of Written Language, Memory tests (for a kid that keeps it all in his head, this is important), and dyslexia tests, and even though you say he has good fine motor, if he hasn't had visual motor integration testing, I'd go for that too. Generally looking at the ability to generate ideas, the ability to put it down on paper physically and cognitively.
FWIW, my dysgraphic has bad writing but the teachers keep recommending GT even if though writing grades are below average. They each explain with a version of "he'd be just as bad in regular classes only he wouldn't learn anything". One said, "he'd get lost there" and another said "his thinking is well above where it needs to be and I don't think his writing should keep him out" So, if you want him to bump up, might consider where he will learn best and be most comfortable, especially if his grades will be the same.
We did keep him in GT up until last year (8th grade) but a GT diagnosis will NOT keep you in honors in H.S. I am wondering if having him in the "regular" English has made things worse not better. The class discussions are so boring that he just tunes out. Can't do anything about social studies, the AP US Class is my school is one of the most time intensive, most challenging class the school offers. And while he would love the class discussions, they amount of homework would be too much.
His English teacher has been trying to help him and getting frustrated as well, I think she is one the same page as I. She really doesn't know how to help him. He did stay with the same teacher despite the "level" drop at semester. I do expect them to say, he's obviously not a "honors" candidate. But this is an example, he tried honors English and did well except for writing and got a C+ in the class. He is not in "regular" English and was doing an A- until the first essay and because of the poetry is not getting a C-. Looking at this grades, I'm not sure it's been a good switch.