Miriam: I’m glad you’ve brought up Germany and China, as they are a perfect contrast to the USA. Those countries have “dialects” with minimal (or no) mutual comprehensibility with the standard (or “standardized”) language, and their speakers naturally struggle to speak the standard accent. In the USA, while Americans are of course capable of hearing the tiny differences between regional accents, the reality is that by the standards of Germany and China (of most countries in fact, including to some extent England, not to mention the UK), all Americans already have the standard accent. There is no need to teach it in school. We would hear more accent diversity taking a train-ride across Shanghai, or London, than a ride across thousands of kilometers of the USA. The USA is “new world” — American English is basically one accent that has spread over almost an entire continent in recent times — the age of mass communication.

@Miriam - Some thoughts on your questions:

1) As Irene and Carlos have said, there's no standard teaching accent. Most American accents are quite easy for all Americans to understand. I don't remember ever noticing the accents of any of my teachers when I was in school. (I was surprised when, as an adult, I overheard a teaching assistant teaching children the word "wash," and pronouncing it as "worsh," which to me is understandable but very non-standard.)

2) Most schools don't teach indigenous or heritage languages, but there are exceptions. I went to 4th grade in Hawaii, and most schools there do teach some literature in Hawaiian Pidgin English, and they sometimes teach some vocabulary or songs in Hawaiian. I also worked at an elementary school in Arizona where the students were almost all Hispanic, and some could not speak English. There were a few bilingual teachers who taught math, history, and science to these students in Spanish, so that they wouldn't fall behind the other students in their education while learning English.

3) I'd say that most types of American English are understandable if spoken clearly, but it depends on the speaker, and also the listener. Also, different cultural groups use different types of slang and idioms, which can be much more of an obstacle than their accents. People who watch a lot of movies, read a lot, listen to different types of programs, travel, etc., are usually familiar with many different kinds of American English, but for people who grew up in one area and weren't exposed to other dialects, it can be difficult.

4) Yes! A relevant anecdote: I took a linguistics class once where the teacher played a video from Jamaica. He asked his students if the video was in English. Everyone agreed that it was not. Then he played the same video with subtitles, and it became clear that every word was an English word, even though the grammar and usage were a bit different. It was understandable -- but only with the subtitles on.

@ Miriam,

The US elementary and secondary "system"'s defining feature is that it's decentralized to an extent that just doesn't seem to exist in other countries. So there are few things that the American public school teacher in general is "obliged" to do beyond essential health and safety regulations; anything beyond that is set state by state, district by district, even school-by-school. There is no Ministry of Education handing down national rules on curriculum or teacher accents.

Americans also don't think about accents the same way the British do. If anything, there was a history of controversy about black English, but that's about it.

Why does the US use Fahrenheit? I always get confused when I talk to an American about the temperature because I always use celsius

@Miriam,

Perhaps I should explain more. The establishment of a national curriculum is illegal in the US. Congress passed a law prohibiting itself from making one.

And that’s not even exactly because of the ideological opposition, which is beyond the remit of this thread, but is covered very well in The Knowledge Deficit by E.D. Hirsch.

The US is a local-control society, and public education is the iconic example issue. American parents expect it and have been vocally unhappy with anything else.