A certain strain of thought contends that cities in the US are handicapped by diversity -- that we will never achieve excellence in education, for example, because our nation has more immigrants than our economic peers. London provides a sharp counterexample because diversity there is driving excellence in education.

So if we could drive excellence in education in America we could have poor students doing well in America too?

Sounds as if the culture of immigrant families is the driver.

  "Wilson adds, 'Aspirations are very high among the families of children with migration backgrounds. That sort of drive really helps them to thrive.'

According to another research report, published by the University of Bristol in 2014, ethnic minority pupils have much higher levels of aspiration, ambition, and engagement compared with other students. When such an educational drive is fostered in a supportive yet competitive environment, the positive results can snowball. Young London residents also have the advantage of higher levels of connectivity, just one of the benefits of being in a large city brimming with opportunities."

Also, I think the headline is misleading, unless I  misinterpreted the piece.  It seems it should be "Why are poor students in London doing better than poor students elsewhere in the UK?"

"In 2002, 22 percent of children who were receiving free school meals—a program designed for poorer students—obtained grades between C and A* (the highest possible grade, comparable to an A+ in the United States) for math and English. Fast-forward to 2013, when 48 percent of children in the free-meals program achieved these results. And the numbers keep improving. On the other hand, gains were much smaller outside London, where the figures [NB: I assume "the figures" are the same figures as above - the marks of students who received free school meals] jumped from 17 percent to 26 percent in the same time period."