Child with ADHD & RSD struggling with unkind kids

[EmDon]

My 9 year old son has ADHD and as part of this has RSD. We are struggling with school as anytime any child is a bit unkind he gets very upset... For example he is at a new school and someone didn't want him to sit next to them so now he doesn't want to go in despite loving it there. He has been bullied in the past but now every small slight is huge to him.
Does anyone have any strategies or suggestions on how to build up his resilience in dealing with other kids being a bit mean?
Obviously we talk to him about it, validate his feelings, try to explain that there are always going to people that aren't as nice as we would want them to be but what can we teach him to do in these situations?

I really feel this, my son is the same, and those little moments can hit them like something much bigger. What’s helped us a bit is giving him simple “scripts” he can use in the moment (like “okay, I’ll sit somewhere else” and walk away) and then practicing those at home so they feel natural. We also talk a lot about “big vs small problems” to help him scale what happened, and I remind him that one child’s behavior doesn’t define his worth or the whole day. It’s slow progress, honestly, but building that emotional muscle little by little. And making sure he has even one safe friend or adult at school, really does help over time.

I'd consider looking at different perspectives - there is a million of reasons why someone reacts the way they do, which are not related to DS. Encourage thinking flexibly. With RSD there's a tendency to assume negative intent, and to react based on these assumptions. If every small slight already feels huge, I'd be careful not to reinforce it further.

Instead of ‘people aren’t always as nice as we would want them to be’ I would frame it as ‘mostly reasons aren’t personal to you’. Unless you know that your child can be overwhelming to other children and give them a reason not to want to sit next to them, then any situation such as the one you have described probably has many other reasons the other child said no. Such as the other child had already agreed to sit next to someone else.

You will know your child best. A lot of this could be difficulties anyone would face in entering into a new environment where they are new and everyone else is not. Maybe ask who he would like to be friends with and invite them round for tea?