To expect my very bright, autistic kid to not fail his SATS?

Agree in the actual exams no one can help with understanding the questions.
But in practicing part of the learning is to know what kind of answer the questions are expecting and what is required. (ie not in a mock test but as part of SATs learning.)

Not sure what you mean by making sure he has understood the questions - a reader can be used but they have to be very careful to use a neutral tone throughout the paper and there are certain rules regarding explaining anything. Also if it's the reading paper then no one gets a reader for this and an adult can just sit there to enable movement breaks if that's what is required.

I would look at why his classwork indicates he is above expected. As others have said, is it because there is less pressure? In SATS is he clock watching/more aware of needing to finish within a certain time?
In class does he actually have more help/support from a TA coaxing him through the work and encouraging him in a way that he wouldn't get in SATS?
Is it techniques that are letting him down? I mean you say he is a whizz at reading and learnt at an early age, but does he comprehend what he has read? (Or is this where when it is picked apart in class he can make good sense of it, but when doing it on a paper alone he struggles?).

I think you need to meet with the teacher to discuss what areas it is he didn't do well on and to see if this is a theme across other papers they have done (my son has done two sets of mock SATs this year already) and also as others suggest discuss the arrangements and whether he needs a smaller room, extra time (did he finish the papers for example as not sure you have mentioned this).

If he has SEN, they can apply for extra time for him, as well as offering a host of reasonable adjustments such as doing them in a quieter room with fewer children, making sure he’s understood the questions, etc. Have you had a chat with him, and separately with school?

I am assuming he doesn’t have an EHCP. Do you think he needs one?

Where did the tutor think the problem lay? Did he not understand the questions? Struggle with the content? Work too slowly? Careless mistakes?

Was he taken into another room to do the test? Given more time?

Whenever my DD has assessments these two things happen and they are proven to make a huge difference to her.

Could your tutor friend not offer a bit more insight? Or could you afford a tutor for a few weeks to work on sats type skills with him?

I agree that it's not worth pressuring kids with sats and don't put a lot of value on them but I don't read your post like it's about that.

I teach at a state school and we have Warhammer club 😅

Have you investigated ADHD? DS1 has both and takes meds in school. He is very focused and scoring top marks at secondary (it was a v different matter in early primary!)

SATS are a measure of how well the school is doing and identify if there are any learning gaps that need addressing before secondary school. Just take the pressure off him & let him enjoy learning.

Is he anxious?

My son passed his days but below what he was capable of. He did brilliant in his mocks as they were positioned as a no big deal, the school ramped up the importance is sats and his anxiety just grew and grew…

Just to add he’s been moved up sets twice now in year 7 at secondary.

I would find out which past papers they used and go through it with him at home. If he does much better at home than at school, then it’s the environment that is causing the issue. If he is struggling with the work at home, you will be able to see which bits are tricky.
is it the maths as well as the English/SPAG?

I think they can withdraw him to a separate room if you think that would help. Let me check the rules on that.

I'm not an expert in any way, but it sounds to me like he's in a transition period, learning about himself and making changes. Maybe his focus on schoolwork has fallen by the wayside?

YABU.

It's normal to want the best for your kids. However, have you taken into account the environment he's in when he's doing his SATs? Environments can make or break success.

I'm not academic at all, admittedly. But do you know when I performed at my absolute worst? In exams, both mock and real. I failed most of my GCSE's because I couldn't cope with the environment. Sitting in a massive hall, having to be completely silent for 1 or more hours. I couldn't do it. I'd often end up having meltdowns and having to leave and do my exam in a smaller classroom at a later date, which still didn't help me to pass them, though my grades when I was in the classroom were higher than the grades I got on exams I'd taken in the hall, but I felt calmer and more emotionally prepared.

If your son's class size is quite large (I don't remember where I did my SATs. Possibly in my classroom?) then could that be the problem?

Is he
. rushing, making silly mistakes
. panicking and not attempting much
. worrying about mistakes and going too slowly
. not understanding the questions
. poor test technique, so getting stuck on a question and not moving on
. not liking the time pressure or environment