You've received excellent advice already - I'l second everything spaghetti said as a start, as well as seconding Portia's advice to ask the mom.
The reason I'd ask the mom - my dyslexic dd had a child in her class when she was new to her school find out she was dyslexic, get curious about it, got some info from his dad, and then tried to "help" her by wanting to be her reading buddy. That was *not* something my dd wanted to have happen at all. Totally different situation than your ds, but I think it illustrates a truth that works with most all friendships and relationships in life - just be a friend. When we want to help in some way and don't know what to do, the best thing to do is to get to know the person we want to help and in getting to know them we'll learn what it is that will help.
You can also remind your ds that he will be (hopefully) influencing the other children on the playground just by choosing to be a friend to this boy. He doesn't have to directly instruct the other kids - just show by example
Best wishes to your ds!
polarbear
