Quick scene setting: Back in September I get a call from the school to say my eldest (10) is fine but has been hurt in, and I quote, 'a completely unprovoked attack by someone he considered a friend' because the boy thought my son had pushed him. I'm told the kid took responsibility, and admitted that he didn't know who pushed him, just turned around, saw my son assumed it was him and punched him in the face, hard. He said he never meant to hit him that hard. 
The red welt was visible for the rest of the evening, and that's with my son's glasses taking some of the impact!
I spoke to the deputy head the next day and she had finally managed to get hold of the boys parents and told me he was being punished. The mum of the boy had lost her mum in the July and posted regularly on FB that she missed her. Despite her being the kind of mum that pulls you up for the slightest little thing I decided to let it go because she had enough to deal with, the kid was punished and I was happy with the way the school dealt with it. I never said a word to the mum about it. But my son stopped walking home with him for obvious reasons.
Now, before this we were never friends, we said morning, that was about it, I'm hardly at the school anyway as I work full time. I do feel she should have apologized for her son's behavior when it happened but you can't force someone to do something they don't want to do.
Fast forward 4 months, yes 4 months with no talk of it, no more drama at school, the boys avoid each other now, and sadly, my boys have just lost their nanny. This morning she shouts 'Morning!' super cheery and barely gave me a chance to respond before she says that we should clear the air. I'm not interested in clearing any air, because I don't think there's any air to clear. Your family hurt mine without so much as an apology so we're done. I'm happy with the current situation of saying hello in a perfunctory tone so no bad air from me.
I said: No, not really, if there was something to have been said it should have been said months ago when it happened. It's over with now, whats done is done. She ignores me and goes on to lecture me about how her son was just defending himself and that my son pushed her son down the stairs (!!) think the teachers would have told me that at the time. I told her what the school said to me, she said that wasn't true and that it must be lovely for me having children that never do any wrong blah blah blah. I told her that not once had I received a call from the school to say either of my boys had behaved badly let alone marked another boys face, shame she couldn't say the same.
She said she didn't know her son had marked my son's face - not sure if she was implying that its ok to punch my son in the face so long as he doesn't leave a mark .....
She was being confrontational and condescending in front my children so I told her that I never called her out on it 4 months ago because she'd recently lost her mum, but now my boys had just lost their nan (funeral last week) and that none of us needed this pavement slanging match. Sadly she didn't offer me the same courtesy and carried on ranting. Even as I told her I wasn't interested anymore and walked away to get the boys into school she carried on shouting at me down the road.
Now I get that there are two sides to every story but my question is this: What parent in their right mind, who has had a call from the school explaining what happened and has a confused son at home with no idea why he was hit by his so-called friend, would simply accept that they are both lying in favor of the boy who caused the red welt in their son's face who had every reason lie? And I'M the one whose boys can do no wrong.
But the strangest thing, why wait 4 months?!?! 
The only air I could have created is by saying 'morning' in a tone that isn't all bird song and happiness. Because that's literally all I've said to her in the past 4 months. And if she doesn't like that then don't bother saying hello then, I really couldn't care less, I certainly won't lose sleep over it, I'm literally just trying to ride out the last 6 months before he leaves the school for good drama free.
Odd how I've heard a few mum's saying they've had trouble with that particular boy . . . .