DS3 was at age appropriate levels up until he was about 7, largely I think because infant education is very "hands on" and visual.
The gap between him and his peers widened as he got older and teaching and learning became much more complex and abstract, and expectations of pupils increased.He was well behind his peers by the time he transferred to secondary school.
DS3 struggled with writing too. I was told this is very common in children with autism, but when he went to secondary school, they allowed him to use a laptop for written work, which he adapted to very well. He is much quicker at typing than he is at writing and it also got rid of the problem of "mistakes". DS could not bear to see a mistake in his book, but an error in typing is easily remedied.
I long ago stopped comparing him to his NT peers and his elder brothers, who both did well at school and ended up going to university. That way madness lies and it is pointless.I just think of what DS3 can do now that he couldn't do last year, or the year before and celebrate those achievements.
Your son is happy. That is the most important thing there is. It means the school must be meeting his needs.
It is well documented that those with autism are at much higher risk of mental health issues than the general population. If they don't have good mental health everything else goes out of the window. Children don't learn at school if they are stressed out by being there in the first place.
There are countless threads on here with parents tearing their hair out over children with anxiety levels through the roof, refusing to go to school, and nightmare schools where they don't understand autism, fail to make reasonable adjustments and regularly illegally exclude children from school.
Four years ago our son was almost broken by a disastrous experience in mainstream FE. Basically they failed him by expecting him to fit in with everyone else. By the end of the year, he had no confidence, his self esteem was at rock bottom and he hid away in his bedroom all the time, a complete nervous wreck.
At one point he was receiving therapy three times a week. It broke my heart the day he told one therapist he was ashamed of being autistic as it caused so many problems for us. (At the time we were fighting an ongoing battle with the LA for an EHCP and an appropriate educational placement.)
DS3 is now 24. He has been at a residential specialist college for students with autism for three years.(We won all three of our battles with the LA.) He has made amazing progress and has finally achieved a level 4 in GCSE English, after 4 attempts. He also gained a level 3 NVQ qualification and successfully engaged in work experience dealing with the public at several tourist attractions.
But he has achieved so much more besides. He has learned independent living skills, and can shop, cook, wash and iron competently and confidently. He is now looking forward to living in a place of his own, when I once thought he'd be living with us for ever.
He has learned to travel independently. When he was 16, I couldn't imagine him ever travelling on a bus by himself. Now, not only does he use the bus regularly, but over the last 2 years he has travelled to and from college, cross country between Staffordshire and Somerset on a regular basis on his own.
Most important of all, he is happy. He will never go to university, but he has regained his self esteem and self confidence and the anxiety that was once so painfully evident, is under control most of the time.