At the New York Times blog The Upshot, Emily Badger and Kevin Quealy have a piece on a new set of data from Stanford University: test scores from 11,000 school districts that have been analyzed to see which ones achieve the most growth from their students.

Way up near the top is Chicago. It's one of a handful in which, based on the scores, students progress the equivalent of six years in just five, and it's the only very large school district for which that's the case. (Schaumburg also comes in above six years.)

This shouldn't actually be a surprise. I've written before about data that indicates this same trend: Chicago Public Schools students start well behind their peers, but then make substantial progress as they move through the system. (Again, this is based on test scores, which are not the be-all and end-all of an education, but it's what we have for a bird's-eye view of American public education.)

I mentioned it in 2016, when the governor said that "many" CPS schools are "basically crumbling prisons." I asked Elaine Allensworth, director of the Consortium for Chicago School Research about that. Here's what she told me:

“We don’t see the schools that are just miserable places to be; that would be very rare now. There’s just been a lot of change in the district. And you can see it in terms of students’ outcomes,” says Elaine Allensworth, director of the Consortium on Chicago School Research at the University of Chicago. “The worst schools way back in the early 2000s, in terms of schools that had really poor educational climates, little trust, and things like that, we don’t see it. Even the schools that are the lowest today don’t look anything like the schools that used to look the worst.”

I also wrote about it back in 2013, when Lupe Fiasco dragged CPS. Despite the district's problems, CCSR research found that Chicago schools do better than other Illinois school districts when it comes to educating children of comparable backgrounds.

And here I am, back in 2012, looking at very similar trends to the Stanford research:

The first thing that’s apparent is that in fourth grade, early in CPS students’ educations, they’re about eight points behind their large-city peers, and this has been true each time the NAEP has been given. By eighth grade, they’ve narrowed that gap, and narrowed the gap with the national average by a few points as well.

As Kim Bellware found when she asked CPS teachers about their jobs for this month's issue of Chicago, many students come in with immense challenges. "People I know from my hometown downstate will always say that CPS kids must be so different from the kids that I taught at the private school there," one told her. "But they’re really not. They’re only different because I never once wondered if the kids at my private school had been fed at home or not."

The data reflects this—academically, they are rather far behind early in their grade school years. By the time they're bound for middle school, they're still below the national average as a whole, but the progress they've made is far above the national average. And there's a case to be made that they're better now than at any point in the past, one that I've argued and one that WBEZ's Becky Vevea, whose job is covering Chicago education, argued a couple years ago.

Badger and Quealy get into some of the reasons why CPS tops the Upshot's list. No one really knows for sure, but the district probably dedicated attention to a number of details rather than one weird trick. The data also suggests some limits on what CPS can do and where its students are still neglected. Even if Chicago is indeed progressing them along better than almost all public school districts, their test scores still end up below the national average in eighth grade because they're so far behind in the early grades.

While the district has made a point in recent years to emphasize its pre-kindergarten programs, it's had trouble selling them to parents. That's perhaps due to parental attitudes in general, rather than the city's specific problems; Americans expect a decent free public education for their children beginning around five or six, and are, generally speaking, required to provide their children with an education beginning around five years old. But before that, during absolutely critical years, it's every family for themselves, a scenario quite different from the rest of the developed world. If CPS is going to make further progress, it may have to start from the beginning, where some of the biggest—yet most neglected—gains can be had.