Of course, 30 years ago when I was a grade-school kid reading Agatha Christie mysteries, I was completely at a loss with "fortnight".
One of the differences shows up in a few prepositions.
In/on the street, at/on the weekends.
The differnces are pretty minor.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
The language isn't called the "English" language for no reason! The only correct version is the English used in ENGLAND. Therefore. As England is part of Britain. The only correct version is british English.
American English is often referred to as "stupidize" by TEFL tutors in Europe anyway. And many people in Europe that use American English in an English exam will certainly FAIL !
I can't see how British English is somehow more correct that American English in America, or Australian English in Australia, etc, etc. There are many correct versions of English- one of the beauties of the language is its ability to adapt to new environments without losing its core comprehensibility.
I have taught in a number of countries and never heard this.
This is factually wrong in the case of the most important exam suites like the Cambridge ESOL ones. They say that, for instance, both spelling systems are fine as long as they are used consistently. It's simply not true to say that an excellent piece of writing would fail in Europe if someone wrote color.
Also, please note that much of your post is insulting and goes against the terms and spirit of the forum. Here all variants of English are respected and regarded as equal. If you find that offensive, then please look for a British-English-Is-Best forum. Our approach is international to reflect the nature of the English language.