"One thing I notice is that when he meets unfamiliar words he is not good at sounding them out - which he was never good at. Same with writing. He can learn things for tests - but does not seem to learn and apply the rules."
DD is in Y3 - she is 7y7m. Sounds like DD, although she picked up reading very quickly within the first weeks of reception. However she sight reads and always did, She will memorise a word once she has seen it and knows what it says. So, when she coems across new unfamiliar words she will guess rather than sound it out. Or she just wants someone to tell her what it is - because once she's been told, she just knows it. Same with the spelling tests I think too, ahe memorises for the test but the spelling patterns don;t seem to stick without a lot (and I mean a lot) of reinforcement.
DD does know her sounds indidvidually but finds it harder to apply them.
"He also still writes some letters back to front often - p, d etc"
DD also reverses some letters and until recently some numbers. She would also write 12 as 21, etc. This has improved massively this year. Wether it is what the support teacher has done I don't know, or if she just grew out of it. I know the support teacher has given her strategies to remember which way round b and d go for example, and I have seen DD use these strategies to check her work.
"often goes blank when trying to manipulate numbers."
I find this interesting. DD is confident in almost all aspects. She will sing solos, perform on stage, do readings, etc. However when it comes to maths she panics and loses her head. She can do it. We have seen her do it and school have seen her do it. She is very logical with Maths - her teacher laughed at parent's evening about how logically she works in Maths. However her confidence in maths ability is zero. She says her mind goes blank and she can't think. This means mental maths can be a nightmare for her as she panics if he has to work fast, esp without writing workings down. In other maths it takes her a good while to relax into it, and remember what her head needs to do, but once sorted in her head she copes fine.
I had never ever considered dyslexia, esp as her reading is so good and always has been. And TBF she doesn't have dyslexia according to the supprt teacher's assessments. But she does have dyslexic type tendancies, which some of the strategies can, and do, help. As I said before, we are already noticing a difference in DD's written work and her confidence with written work this term - after just 1 few weeks of 20 minutes sessions a week. She is writing way more and etting more of her fab ideas down on paper and presented better. I know we are lucky that it was picked up and noted, and even more lucky that the school have acted upon it. I know she wouldn't have got the supprt in many schools for her level of difficulties.