memhegan,
have you talked to your son's teacher this year about your son's problems? if you put the name of a disorder to the teacher, it might help him (or her) to skip past or out of his confusion.
i think i understand what your son might feel as he tries to write and can't. i explained in my first post that i'm sort of the opposite - writing is easier than speaking - and i explained the darkness and depth of the depression that could come upon me when trying to do what was necessary to limp through english (a necessary subject to complete year 12 and get into university before age 25 as an adult student). if your son is anything like that when put to the task, i know exactly how it feels. it was only when she saw this happen to me that my mum fully started to understand what was going on and how serious it was. i don't recommend it (it's really unnecessary to put your son through it; it costs too much to him), but if your son does this, then show this to the teacher. maybe then he'll understand that it's not just laziness or unco-operativeness or anything trivial like that that stops your son from working up to his age level with writing or typing.
i feel like i should explain what goes on in my mind when i try to speak, rather than write. i explained in my first post something of what goes on when i try to listen.
generally i find myself composing a sentence in my head, often not a whole piece at a time (somehow i can't quite hold it all in there at once, and it works the other way, listening and oftentime reading as well). i then write the first part of the sentence, [pause] (i'll keep doing that to show what it's like [edit to add:] even if it makes this paragraph terribly hard to read) [pause while i regather myself and go back to the beginning of the sentence] which gives me a solid place to hold it, rather than ephemerally in my brain as i search for words to express the meaning of the rest of my sentence (clarifying it as i do so), [pause/recollection] and am then able to write the rest of it and conclude it. when i speak it, i usually have pauses partway through my sentences, or [pause] end up cutting them short or losing my point along the way. [long pause] it puts me at a significant disadvantage in conversation or debate. it makes me unable to respond intelligently to a lot of what my friends are saying, because i'm trying to interpret their words, try to gather what i know on the topic at hand, figure out what's relevant and how to phrase it, run down a few threads of possible responses and all too soon the moment is lost and i've sat there in silence waiting for someone to pick up the lost thread somehow or change the subject (or i end up doing it).
GAHHH!
sorry, that's how frustrating it is. :\
when i was at primary school, i had something of a stutter in my speech, as well as a deep slowness. after i went to high school, my social situation changed (for the better) and my stutter disappeared. i remained (and still do remain) a slightly slow speaker, and also a very quiet voice (perhaps also partly due to a lack of nasal resonance). often, now, as i continue to grow up (even at 21

), and [damn, another pause

] continue to expand my brain and neural connections i can find myself thinking faster than i can make my poor larynx and tongue work to output words and i stumble over them. sometimes i go too slow for them and start to stumble as i try to keep up.
back to the issue at hand: your son.
if you can arrange writing and/or typing practice for him regularly, he might be able to improve. it's important, however, not to ask him to go past his limits, because that will only take him backwards and cause him to resent it.
in the meantime, until his writing skills are improved (and even, or especially, if they don't improve much or enough), see if you can give him a tape recorder for assignments. something that can complement his brilliant ability to speak that his writing disability doesn't interfere with his learning or his enjoyment of it.
as for his inability to really make friends... anything i say is going to be cold comfort, alas. like i've said previously in this thread, there's not a great deal to do about this except for letting him grow up and meanwhile teaching him about people and how they work.
there are asperger's support groups and classes that i've heard of where children (and adults) are taught specifically about socialising. if you believe it's necessary, see if you can find something like that locally. i don't know what actually comprises those classes, but it may be that your son just won't need it, or he might turn out with a better social understanding without them (he could possibly turn out as a social "drone" walking the walk and talking the talk, but not fully understanding what it means; just socially conditioned). i can't say, as i never had any such classes, what that case will be or if it's even necessary. though my social insight is still lacking, it is improving with age.
anyway, i hope i've helped somewhat. i guess all the positive feedback so far means people are appreciating and getting something from my rants.
lank