"DS is adopted and definitely has some attachment issues but I am fed up making excuses for his behaviour - he has to behave simple as that."
The fact that he is adopted is very, very important indeed. I think that it makes it even more important that you do not carry out school's agenda at home by punishing him. I'm not sure how old he was when he came to you, but home is where loving, secure attachments are made, and punishing him for behaviour he is exhibiting at school could seriously impact on this.
Put simply, the school are failing him. If you do what they say by punishing him at home for behaviour at school, then you could be unintentionally colluding with their failure.
It makes me very angry that support in school for adopted children all but ceases once they are adopted. None of their issues disappear! I am an advisory teacher for Looked After Children, and Part of my job is to work with schools to put in place support systems for children who are struggling with behaviour. Of course, what works will depend in the child, there is no one strategy which will work for all children. Having achievements recognised verbally for example can be counter-productive for some children who have suffered neglect and/or abuse, as they have no idea how to react, and engage in familiar, often destructive behaviour instead.
I would be asking for a meeting with the school's Designated Teacher for LAC (every school just have one), and working with them to design a behaviour plan which lists his triggers, behaviours, and effective strategies for dealing with them. I would also be asking the SENCo to attend the meeting, as he should be on school action at least. I would be ensuring that he had a 'key person' to go to at school; be that the DT, learning mentor or TA (not the class teacher), and that this person received training on attachment issues.
Since your son's early life was problematic (I assume; please correct me if this is not the case), the idea that he 'just has to behave' is erroneous, as he missed out on learning key things as an infant (security, having immediate needs met for example) which would enable him to behave appropriately. It's important that his school understand that he does not need to 'relearn' how to behave, he needs to learn from scratch. Just because he behaved appropriately last term, or at home, does not mean that he 'knows how to behave' IYSWIM. He may have difficulty trusting new situations and/or generalising his skills.
You know much more about your son than the school do- please don't follow their lead when it comes to addressing his behaviour.