OK - my own backstory is most likely informing my view on this but this is how I read the subtext of these comments from the teacher:
disengaged and difficult to read. He is very sensitive and doesn't like
to be wrong so avoids challenge.
Your child is trying to be neutral in class (most likely to avoid getting into trouble or being shouted at). When the teacher tells him he's got something wrong he finds it upsetting - so he is frightened to get things wrong.
I'm not sure how old your DS is - but up until about 9 getting a lot of sense about what goes on in class is really difficult.
Try asking your DS does your teacher shout?
Is there a lot of chatter in class?
Is there bad behaviour in class?
(if the answer to all 3 of these is yes - then it may be that the class is fairly 'lively' and perhaps there are times when the teacher struggles to maintain order - this may stress the teacher and more sensitive children get upset when a grown up shouts at them, especially if this is fairly unusual at home).
What happens if you make a mistake? Does your teacher explain where you went wrong and help you to understand what to do next time so you get it correct?
This is really important. DD2 would get things wrong and be told she wasn't reading well or had made a mistake on a calculation but often would not have it explained. Worse yet a few weeks later she'd be moved down a table - very publically, which she felt was totally humiliating. Unfortunately the class also had a few characters who really enjoyed needling children who were struggling - Ooooo you can't read chapter books, you're such a baby! and such. DD2 felt almost paralyzed anytime she was asked to do something new or a little difficult - because she was terrified she'd be moved down a table (and lose access to interesting class work) or she'd be teased.
I'm not saying this is definitely your DS's situation mrsnw - but it's possible.
His writing is not punctuated and he writes reams and reams and none
of it makes sense.
Well this is resolvable. You can work on this at home. Start with something simple. Like full stops or maybe getting the spelling right on a word he frequently misspells (for us it was whith for with).
These VCOP (vocabulary/ connectives/ openers/ punctuation) pyramids really help you to see the logical progression of punctuation/ vocabulary skills in writing. The top of the pyramid is easiest use of language and the bottom is more advanced/ skillful use of language.
VCOP Link: displays.tpet.co.uk/?resource=387#/ViewResource/id387
The none of it makes sense comment is pretty harsh and fairly unclear - is it illegible? are the spellings so wildly out they're hard to work out? is it just stream of consciousness? I think you may have to look over what your DS is writing and see if you can determine where the issue is.
If it's handwriting - well that can be resolved through practice - Collins handwriting books are brilliant (try large newsagents/ book stores/ amazon) - sometimes the transition to joined up writing can result in a real downturn in quality of penmanship.
If it's spelling attempts are crazy - well gradually start to work on that. It may be that he sees no rhyme or reason in why words are spelled as they are - so work on sounding out words in an overexaggerated way - to help with spelling. Work on rules (which of course always have exceptions) - but i before e except after c, double consonant if the vowel before it is short - so stop becomes stopping to indicate the 'o' is a short sound - not long o as in cope to coping.
stream of consciousness - well this is about organising your thoughts and planning out your work a bit better (thinking of who you are writing for and what you need to explain). Often children don't realise that adults may not appreciate the finer nuances of Pokemon lore - so we need to know who is the good guy and who is the bad guy, who is kind and who isn't - or a lot of what is discussed will make no sense.
Anyway - I've pretty well written a small novel - so I'll sign off but I hope that helps.