Actually, the impact that standardized language education has had on dialect variation isn't quite clear. It appears to have had some impact, but not as much as

Actually, the impact that standardized language education has had on dialect variation isn't quite clear. It appears to have had some impact, but not as much as laypeople usually think. In fact, standard written American-English has undergone quite a few changes over the last 100 years and things that were non-standard have become standard. Likewise with mass media. There is no evidence that mass media has had any effect on the rate of linguistic change and variation in America. The biggest impact has probably been the increase in ease and speed of modern transportation. Regardless, there is likely more dialect variation in America today than there was 1-200 years ago, though geographic variation may be slightly diminishing (at least intraregionally) and socioeconomic variation may be more important. The biggest factor in dialect development is time, which is why you see a large variety of dialects in England as compared to the USA. England is much smaller, but has had much longer for dialects to develop.