My mum used to correct speech, not written but spoken; she would actually interrupt me as a child when I was trying to tell her something and it inflamed me. I can still feel the pain of it!
What was so ironic was the fact that her grammar and speech was awful, she strung her vowels out on a clothes line. She said things like, "Them", instead of "Those", oh I could go on forever. If I went out with her as a child and we met someone she vaguely knew, she'd put on a fake accent which was dreadful. She was just pretentious, a typical working class snob.
I wish I'd said nothing now, it's upsetting me to remember.
I didn't do that to my son, nor did I allow her to do it to him, but obviously we have to gently guide our children into understandable speech (nothing to do with 'posh' whatever that is), and a reasonable standard of grammar. School does that too, I've no complaints. My son has grown up to be himself.
This will sound odd to many but I am quite upset now and it was all a long time ago. Of course she was good in lots of ways, please don't think I didn't love my mum.