Language changes and all that.
But I've been trying to make sure my DC learn standard grammar, even if some forms are in a state of change. My argument is that it's better to learn to say "could have" (not "of"), or to know the difference between "less" and "fewer", because one day in a job (or other life) situation they may come across a pedant who will judge them if they are not using standard grammar.
DS thinks I'm a pain in the arse, (although he's not allowed to actually say it in those terms
). He keeps reminding me that I've also told him that languages change.