M.L.
Do boys ever understand gentle terms?
But you could say, "Well, this is the time you boys get to find out what being a friend is really about. Sometimes you will both like each other, and sometimes you won't. It's good to have a lot of friends at school, so when one of them is mad at you - like James is right now - you'll have other kids to play with. In a few weeks, things may change and you two will be buddies again. But for right now, give James time to get over his "mad" and enjoy the other kids." "But I want James to be my friend NOW!" "Friendship can't be on the basis of just what you want. The other person has to want to be friends, too. Give it time, and when you come home from school you can tell me who you *do* play with right now."
Worth a try, anyhow. What the other boy is like doesn't need to enter in.