I'd sleep on it.
Then try to take the approach that you are acting as a "court recorder" as you mentally walk back through everything you can recall about the meeting.
It sounds as though there are two problems:
a) your son's disability is unfamiliar to the teachers (and possibly the administrators)
b) your DS is perhaps about typical in terms of
agemates and maturity-- yes? Well, then, they may be expecting a level of MATURITY which isn't really appropriate for his asynchrony-- and that is a separate thing from his disability. That's gifted asynchrony.
Finally--
is it possible that your DS is behaving in ways that are exacerbating the latter problem? It sounds
plausible from the comments you reported-- "making noises" and out-of-turn talking, or the proposed "learned helplessness" strike me as possible red flags indicating frustration with behaviors that teachers are seeing as disruptive. I can see how a student who needs to conduct most work orally, and is accustomed to doing so, could seem "immature" or even "needy" to a classroom teacher who is
also trying to meet the needs of 20 or 30 other young students.
That doesn't make it right to dismiss very real limitations and accommodations that they demand-- of course. But it might help to try perspective-taking before writing, so that you can cultivate a non-accusatory tone in the writing. Ask yourself WHY they are seeing your child in this way, assuming that they are rational professionals, and not trolls who live under a bridge and seek to harm children and parents at every opportunity. (It is at least
somewhat more probable that the former is the case, here, right?)
Okay-- then write it ALL out. ALL of it.
Now revise and remove emotional content-- use Wrightslaw's Letter to a Stranger if you need help there.
Trim things up so that only really awful/discriminatory or somehow actionable items (proposed changes, judgments about ability or appropriateness) are left; because that is what you want highlighted in your letter of understanding.
How can you help them to see BEYOND what they currently think? That's what you have to do AFTER you have that letter of understanding written. Now read it again, and ask yourself if anything is going to interfere with that ultimate goal.
At least you learned what you're up against. Right?
Good job keeping your cool in that meeting.