Explaining diagnosis to a child

Hi all. My son will be 9 next month. Nearly a year ago he was diagnosed with aspergers and dyspraxia. He has just started to ask questions about why he gets extra help at school and his friends don’t. I’m just wondering how best to explain it to him in a way he’ll understand. I did try to talk to him about it after the diagnosis but he changed the subject and didn’t ask again. Neither condition has been explained in any great detail to us and I’ve found a lot out from the internet. Thanks