My two-penneth on the Great English Teaching kerfuffle 2020:
1. Prescriptivist grammar teaching IS problematic, see the KS2 Grammar test which is prescriptivist AND pays no head to stages of child language acquisition.
2. Descriptivist approaches to grammar is the approach

Linguists and Stylisticians take - eg What does ‘x’ do in ‘y’ context? It looks at grammar and its usage according to context - and it’s also the approach of Lang & LangLit A-Levels. You have to ‘beat out’ the concept of ‘correct’ grammar in those kinds of A-Level classes.

3. Spoken Language has its own structure(s) and grammar(s), it’s just different from writing. I’ve added plurals as the structure & grammar changes according to context.
4. ‘Correct’ really isn’t the best term to use when properly examining grammar, but MAYBE ‘expected’ would

work better in the context of this latest kerfuffle. ‘Standard English ‘ is expected by exam boards and in many situations outside of school so contexts, a, b, and c expect SE, but context f and g doesn’t (it’s not expected - see?’)

So in short ‘correct’ - is not a helpful term to use re. grammar & language usage, but what is probably more useful is framing it as ‘expected’ or ‘unexpected’ or even ‘appropriateness’ and ‘inappropriateness’.

*maybe ‘not expected’ is better