It's "ow" and "garn" that keep her in her place,Not her wretched clothes and dirty face

Standard English is important for business and social reasons, but you should not be a grammar policewoman 24/7. In fact there are benefits to speaking another "dialect" in one's home or local community. [bold added]

All children in Britain and America do need standard English. But they do not need it all the time. Indeed, there is absolutely no need for them to abandon their home speech; people are perfectly able to switch speech varieties. Watch the many talented black American comedians, from Richard Pryor to Eddie Murphy to the duo of Keegan-Michael Key and Jordan Peele, whose effortless swapping between a buttoned-up English and black vernacular is played for laughs. For plenty of people this is a survival skill, one that deserves respect. Fortunately, it can also be taught.

The core of doing so is recognising how language varies naturally by occasion. Both teachers and students should be taught to think about this variation with curiosity. If both dialects and the standard are valuable, what is interesting is just when, and how, people switch between them.

Amazon sells the 1959(!) edition of the
grammar book I used in school.

Everyone in my neighborhood spoke pidgin ("do you want to eat?" is you like go eat?) and my young ears instantly picked up on the difference between how I should speak in school and how I should speak with some of my friends. It's all about being accepted, as I bounced back and forth between pidgin and "haole" English depending on the context. (BTW, I am envious of Chinese and Mexican kids who talk to their parents in their native tongues then switch to accent-less English at a moment's notice.)

Our society generously rewards those who can not only empathize but adapt speech to their audience. It's part of salesmanship, in other words.