This Quora question has been answered by several people, in several different ways. One stood out because of its 'holier-than-thou' attitude. This person said that he did well with no preparation because he grew up without a TV and read books all his childhood. (By the way, I too read just as much as he claims to have done, and I still managed to fit in some TV-watching and generally being a well-rounded person. But that's not relevant.) He also said this:
I had an English teacher as a mother and a proper British grandmother correcting my grammar.The English teacher as a mother, fair enough - that might help you to do well on the written part of the test, as she presumably knows what's involved and how to do well. But the British grandmother part is just plain wrong. (Not wrong that he has a British grandmother; I'm sure he does. His assumptions are wrong.)
Firstly, there is the implicit assumption that simply because she is British, or 'proper British' as he says, her grammar will be impeccable (read: Standard English). She might well speak absolutely Standard English, with no non-standard forms whatsoever. If she does, it is not likely to be because she is British. She might just as well do that no matter where she was from. There is some idea that 'British' grammar (FYI: no such thing) is 'better' or 'more correct' than US grammar. It ain't true. The chap answering the question did mention that he reads fantasy and plays RPGs, so perhaps he's basing this on Lord of the Rings. Or perhaps his grandmother also believes this. Whatever.
Secondly, even assuming his grandmother does indeed speak Standard British English and knows all the prescriptivist grammar rules, if he follows her British conventions, some of what he writes will be marked incorrect in the US. For instance, the title of this post lacks the Oxford (or serial) comma. That's standard British English. In the US, that would get a big red mark. Using plural agreement with grammatically singular but logically plural referents is OK in the UK, but not the US ('the government have/has announced...'). I say dreamt; an American might be more likely to say dreamed. I say a bird shat on me; an American might say it shit on him. I say I have already eaten; a US speaker might say she already ate. I say that the event will take place on Monday; a US speaker might say that it will take place Monday. Hyphenation and compound words have different rules. I won't go on, but there's a list here if you're interested.