I guess as Grinty says the ideal would be a class full of kids his age that are working at a higher level and given that the education system is not going to go back to streaming anytime soon I guess we just have to work with what we have.
Wouldn't that be great? Like you, most of us don't have that option, though! Maybe the difference on our end was that our dd12 skipped a grade later in the process so she had more time to physically and mentally mature before being placed with much older kids. She was always with somewhat older kids b/c her bd placed her on the younger end for grade, but it wasn't as big of a gap pre-skip.
My dd has always been an amazing writer in terms of concepts (what she writes), but the physical act of writing was a challenge for her early on and I do admit that I took transcription for her at times when she was younger b/c she was so slow getting it out on paper. We also worked on typing and she is a decent typist.
She did have trouble with physical output and also with peers understanding her at your ds' age. She was dx with dyspraxia and SPD after her IQ testing although I don't know if they are truly issues she has. She's outgrown them enough as she's gotten older such that they really don't present a significant challenge for her anymore. We've contemplated retesting IQ and I'd be curious to see if those parts that were impacted by anxiety and slower speed like the block design test would be higher now (I suspect they would), but I think that we've decided against it. It really wouldn't make a difference in anything she's doing at this point.