I feel for you pink because I remember how difficult things were with my own DS in Reception and Y1 and 2.....it was at the end of Y2 they diagnosed autism and a year later ADHD. I am also familiar with the "bad parenting" accusations which are unhelpful and make an already difficult situation worse.
My son is on the higher end of the autistic spectrum so he can talk (the hind leg off of the proverbial donkey) and is affectionate and loving. He is also now achieving average in academic attainment for the first time ever....at 9 though he still has a place he can go to "get away and calm down" which is the finance admin's office.....she keeps a beanbag on there just for DS!
In the classroom he still retreats under the desk if overwhelmed.
Even without the diagnosis though his school were supportive, they put in 15 hours of 1-1 time for him from their own budget...something I will always be grateful for.
I am not saying your DS is autistic or has ADHD, it might simply be a maturity thing but the sensory stuff can be overwhelming for some children, bright lights, a noisy classroom, over sensitive to touch etc. It might be these things are bothering your DS but at his age he cannot verbalise this easily.
Definitley the SENCO needs to be involved to find a way for your DS to stay in school. My DS's school only exclude as a last resort and then they make it three days while they approach the special needs people for support...the whole idea of exclusion should not be punitive...it should be for everyone to have breathing space, take stock and find a way to support the child so exclusion is not needed again.
I hope the SENCO can support you....it's pointless them sending your DS home if they are not going to address the issues which are causing problems. They need to be finding a way for him to access the curriculum.