Thanks so much for all the replies, there's a lot of food for thought here.
The SPD was diagnosed by an OT after doing a SIPT assessment and after we'd filled in a sensory questionnaire. He had quite serious modulation issues, but after about a year of OT with a great therapist, she graduated him as she said he was soaring through every challenge she was setting him and there didnt' seem to be anything problematic that needed more work. He did The Listening Programme for auditory processing while he was in OT.
The mystery here is this:
He decodes very well (phonics are really strong)
He spells very well (will write out spelling words 2-3 times in a week as part of the set homework, he doesn't study for the weekly test, and still gets 95-100%)
His verbal score pulled down the non-verbal - think verbal was 128, non-verbal was 136, overall was 132.
We did suspect a possible expressive language issue - however we are a bilingual family, and this seemed to resolve itself? When he was still in OT he would often just say "Never mind" as it just seemed to be too hard for him to put words together to express himself. He says ummm a lot, and he used to describe a word instead of using the word and then go Oh! YES! when we supplied it for him. Once on the way to OT he said a string of words that made no sense whatsoever, then sighed and gave up. This did improve a lot when I told him I'm happy for him to take a breath and think through what he wants to say, I can wait. This is much better now.
I did wonder about stealth dyslexia - the visual assessment basically resulted in us being told he is working about 3 x harder than he should be - but there has been a definite improvement in terms of losing place, replacing words, skipping etc. It still happens on occasion, but generally when he's not wearing his glasses/is tired.
Blackcat what you say in terms of he just simply doesn't seem to know what to say/write rings true with me. I often feel like he has the vocabulary department of his brain, but the writing/planning part of his brain doesn't seem to be working together with the vocab? I don't know if that makes sense.
My nephew has been tested and has Aspergers. DS did a number of austistic-type stuff when he was younger, but a lot of it seemed sensory related (eye-contact, not liking hugs).
Maisey and ElizebethN - the pattern you describe seems pretty familiar.
My question would then be - did getting the diagnosis help you in terms of helping them? I'm not hunting a diagnosis for diagnosis' sake, I more just want to know if there's something that we can look at and go ok, so we need to really work on building x and y, we have to explicitly teach these skills, he will probably always need help with b and c, type thing. I just want a better picture so that I can help him not be frustrated by - well, life - unnecessarily.
Platypus, we've been told he's a dual processor, so he tends to fiddle a lot while being read to, which makes it hard to know whether he's really listening, but I'd say that when he is listening, the comprehension is about the same as when he reads the story himself?
Thanks again for all the replies, I really appreciate it!
