verybusy spider, I know exactly how you feel. My daughter had all the same behaviours as your son when she was his age, she's 21 now.
At the age of 5, after I had to beg for her to be tested, she was diagnosed as having glue ear and had grommets fitted....they didn't work. I won't tell you the very looooong story (unless you want me to) but after much shouting at people she was diagnosed as having a bi-lateral sensory neural hearing loss (nerve damage) and I was devastated, I had never even met a deaf person before.
she also has dyspraxia and other issues. My youngest DD is also deaf but doesn't have any other problems ( hereditary)
As I said earlier she is 21 now and at uni studying to be a vet, has come top in her year and passed all her exams with a first. She still has problems but nothing is insurmountable.
Your son might not have a permanent hearing loss, but please don't underestimate how not being able to hear will affect his reactions and integrations with the world.
The school are handling it very badly and letting you and your son down, don't let them. I know how hard it is to take all the negative stuff....it does get better I promise.
I love that you have told the school that you don't have a problem and told them how you would do things, it shows how in tune you are with him, you will be making adaptations to his 'traits' probably without realising, and making his life much easier at home than it is at school.
I am astounded that the school are not taking on board his hearing issues. If he has glue ear at best everthing will sound muffled, no wonder he doesn't always engage he may not be aware of what's happening around him, and at 4.5 he is still a baby!
Once my daughter was fitted with hearing aids all her 'different' behaviour stopped, although she had problems integrating socially for a long time.
I don't know if any of this is relevent or helps you, I just wanted to let you know that I know how you feel and that there is always light at the end of the tunnel. If you need to chat, let me know.