individual SATS results also follow a child right through secondary school as well
Two of my DC didn't do SATS. Even the one that did sit them went to a senior school where CATS results were used rather than SATS.
Dickory, it is very hard, I know. What many people don't appreciate is that a child with SEN has to work much harder to obtain the same result as their peers. Their true intelligence can be masked by the SEN, and this can be hugely demoralising for them.
Could you ask the teacher to email you with confirmation of the homework each week, to avoid the confusion?
If your older DC went to bed a little later, would this give a chance for the younger one to fall asleep, first? Perhaps that extra half an hour could be used for reading time. Some of the suggestions here are good. You could read more to him, or try page and page about? Also, reading together, (so you both say the words out loud at the same time) can work quite well.
Have a look at Toe by Toe. I did this with DS, and it really seemed to improve his reading age very quickly.
Could a tutor help? DD2 went to a tutor (a retired teacher) who helped her with her spellings and maths each week. She also did fun stuff - DD2 is good at geometry, so she would pop some of that in, which was very encouraging for DD, to see something she really could do well.
Just some ideas. They might not work, but they're things that have worked with my DC.