Yes. Apologies are hugely important. It may bring your DC a sense of peace. Your DC must have been pretty traumatised to be avoiding the letter though. Don't push it but maybe leave it somewhere, like on the kitchen table, and inform your DC that you'll leave it there for him/her to read when he's/she's ready. Your DC has moved on/coped in his/her own way, I imagine. But maybe the letter will help your DC feel more relaxed/less threatened at school.
after they have said that they don't want to read it?
They have given you their answer. They (the victim) do not wish to read the apology. You shouldn’t force them. They have the right to decide whether they accept or acknowledge apologies from their abusers. If you want them to see how to accept an apology and respond gracefully then you model that for them in your behaviours. You don’t force them to accept it on their own relationships. That would also be a form of bullying.
I think it depends on the incident. Was it a one off? Was it a sustained campaign? How old are the children involved here and how did the apology come about i.e. Is the instigator genuinely apologetic or were they forced to make the apology by someone else?
There are far too many variables here to be able to give a one size fits all answer, although I do agree that being able to accept wrongdoing and to move forward is an important life skill as much as being able to apologise and recognise wrongdoing is also an important life skill.
I'm with Donny. No obligation to accept an apology. Especially a forced one. A bully lied about apologising to my DC and the parent got involved saying my DC had to accept the apology (which hadn't been made). DC just said they wanted nothing more to do with the bully and I supported that. It's not a very popular move but I believe it's an important life lesson. We don't try and tell adults when they have to make up.
How long ago was the apology made? IMO the best apology is changed behaviour. I would keep the apology in a drawer and allow your DC to see how the bullies treat them from now on. If in a month or so your child feels they are being treated well they may be in a better frame of mind to read and accept the written apology.
Sorry. I see it has already been a month. I’m guessing as your DC still doesn’t want to read it they were either really traumatised by the bullying or they just have no desire at all to have anything to do with the bullies. Which is a valid choice. I would respect their wishes.
Don't make him read it unless he wants to. You can let him know it's there. It should be his choice. He's been through enough. Also, we need to teach kids how to apologise and how to accept an apology, but at 12 kids know what they are doing. A forced apology is an empty apology and gives the power back to the bully. Let it go.
My son was bullied by several kids, but one mum was insistent that we "get the boys together to talk it out". I said no, I wouldn't be forcing him to do that, and she completely lost it. I think she felt like the victim because her perfect little child was called out for not being so perfect. She was a bully herself. My DS didn't want to and was trying to put it behind him. I respected his feelings.