in which country is American English taught in school?

Canada speaks american english and writes british english.

The US has several protectorates like philipines, panama, samoa, guam, puerto rico and so on. They likely speak American english there.

American english is taught mostly in America and Japan, but China and South Korea also may have the americanized style [I'm not sure].

The truth is, the english language is disorganized and written/spoken in many different ways due to the rival historic colonialism of Britain and the United States.

Canada speaks a variant of English called "Canadian English" that is almost identical to American English. It sees like Japan, South Korea, the Philippines, Latin America, China, etc. seek after more of an American-style English while must of the rest of the world still teaches British English.

Only British and American English seem to be the prestige variants of English -- but that's just my opinion.

Presumably in the USA. Certainly not in Britain, Australia, etc, as part of the normal school courses for children in those countries.

But note that the English spoken in Australia, South Africa, Kenya (note spelling), Canada, is somewhat different from British or American English. The English spoken in India, parts of Africa, the Caribbean and other places can be very different from the English spoken in Britain or the USA. Even the English spoken in the north of England differs in vocabulary and Grammar from that of southern England; to some extent that applies to the USA as well.

Many years ago in Austria I saw an advert for teaching "American English".

In Germany, American literature is taught in higher educational classes, preparing you for university (which, in our school system is 11th and 12th grade advanced course), and unavoidably, that will influence you towards a more American style. And as far as I know, both British and American spellings are considered correct in written exams. So if you write "traveling" (American) or "travelling" (British), "color" (am.) or "colour" (br.), it shouldn't matter.

Of course, as we're Europeans, British English is still the kind of English that is taught in schools, with all of its strange spellings, but most students adopt the American way nowadays, or make up a mixture of both, like I sometimes do. I call it "continental English".

It really depends on Geography, and International Relations.

Most European nations learn British English, for obvious reasons.. So do former British Colonies and Nations with strong ties (economically, particularly) to the UK.

Likewise, nations close to the US politically, economically, etc (S. Korea, China, Philippines, etc) learn American English.

Russia, China, Brazil (mostly). It is a matter of choice between practicality and snobbery (particularly cultural snobbery). As we Brits ourselves have observed: "the brain drain goes west but the snob drain comes east". The real tragedy is that anyone anywhere (outside perhaps Edinburgh) feels obliged to learn or use any sort of English, period. Of all the world's major languages, it is the most imprecise, slovenly pronounced and crazily spelled, useful only for politicians, sales people and confidence tricksters to waffle, equivocate, and obsfuscate in, and second rate comedians to use to make the cheap jokes of puerile word play. Even in its forte as a language for snobs to employ to make subtle, patronizing, social distinctions it comes a poor second to Parisian French. I grew up speaking it as my mother tongue (mostly in S.E. England and the American Midwest), and, 86 years later, I have yet to master its grossly overloaded vocabulary and still have to consult a dictionary to ensure that my õrthographical choices conform to an uncertain norm, based, more or less, on the pronuncaition of our first printer, the late 15th century William Caxton, as differentially modified by Sam Johnson in 1755 and Noah Webster in 1811....

Mexico.

There is no such thing as "American English". It's all the same language, only the accents are different.

Japan, but it often isn't taught well.