(...) should schools encourage and assist some children modify their
accents, or become multiaccented?
On what should be taught about spoken English in
the 21st Century: more questions than answers. Neil Mercer, Director of the Centre for Research in Education and Educational Technology, Open University.
I wouldn't be opposed to that... You mean like how in Germany everyone speaks their own dialect but knows Hochdeutsch as well?
At least in the area I am from (Wisconsin, even though this seems to be typical of much of English-speaking North America), spoken English is not taught at all. I myself support this type of position, and would be against teaching spoken English to native speakers in the first place. Such is likely why many North American English dialects have survived better than, say, many High German dialects (outside Switzerland). As opposed to, say, in High German, what is spoken in many areas of North America is simply thought of as how the native language of the area is spoken in a particular region, rather than as dialects in opposition to some fixed standard. (There are notable exceptions to that, though.)