Not really that impressive IMO.
Just grabbing one highly adjusted score and drawing conclusions solely off of that is not enough. It's really only giving you one piece of a very complex puzzle in the case of something like education scores.
Observational stats in social sciences turns out to be a lot like epidemiology and strongly held conclusions are hard won.
Generally speaking in order to evaluate the success of a school system you really do want to adjust for the demographics that that school has to deal with, so you don't attribute the effects of, say, private tutors to the public school system. It would be really unfair to judge teachers in the Bronx for their inability to compete on raw scores with teachers in upper Manhattan.
You don't see the issue?
When you're measuring schools you're trying to measure the impact of the actual school, not all the other factors, and to do that you have to separate out socioeconomics. Higher income parents are more involved in their children's education and can make up for a bad school in ways that lower income parents can't. It's pointless to compare schools to each other unless you adjust for demographics.
The correct approach is to adjust for demographics but do so carefully, rigorously, and consistently.
You want to measure the impact of educational policies on students. So you control for other factors that influence educational outcomes, and you try to eliminate those effects.
Girls do better than boys on most testing. Asians do better than other races. Free & reduced lunch kids do worse. Special education and ESL students obviously do worse. So of course you're going to adjust for these populations.
The only reason you look at the raw scores of a rural district outside Biloxi that is 70% black and compare that to the raw scores of a suburban San Francisco district that is 50% asian and 35% white is that you either don't understand math or you're more interested in making a political argument than an educational policy one.
As other commenters are saying, Mississippi children's actual achievement rates are still bottom of the barrel. So while they might be statistically doing better, they're not actually doing better at the moment.
That's not to say that things can't turn around, or that this newfound investment into education might not bear fruit very soon.
But the OP made the choice not to address any of these issues; therefore, the article doesn't seem to have been made in good faith relative to the HN community's expectations.
Mississippi's kids are doing 1.5 grade levels better in reading than they were 20 years ago. That's an objectively good thing. Maine's kids are doing 1.5 grade levels worse than they were 20 years ago. That's an objectively bad thing.
It makes sense to look at why.
You'd have to do something like take the high-performing SF district and give half the students, randomly selected, free lunches.
Nonsense, you end up with results like "free and reduced lunch programs are correlated with kids who do worse", which they absolutely are!
I think it's partly because political conservatives are more often right when it comes to education, because they don't listen to the experts and just demand boring conservative things like phonics, learning the times tables, learning facts, and other stuff that "doesn't really teach you how to think".
Just have a look at what the Harvard Education Review thinks is important - https://meridian.allenpress.com/her - no that's not a parody site by someone who uses the word "woke" without scare quotes.
Progressives listen to experts, and the experts in education are often a bit ... scientifically lightweight. Teachers are not all brilliant at scientific research (nor do they need to be, and expecting every teacher to be a scientific researcher would drastically limit the talent pool, or require a very significant salary bump to get more candidates), so universities need to cater to the lowest common denominator, which makes teaching degrees mostly a course in using education jargon to write persuasive essays.
If you have scientifically lightweight uni courses, you tend to get a lot of scientifically lightweight researchers, who are far better at writing a persuasive essay than actually looking at evidence. And with a critical mass of lightweights, they don't really want education to move into a more scientific or evidence based footing, because then their own influence and maybe even careers will be harmed. Yes, there's good education researchers, but most of them work in Psychology departments, not Education departments. Or special education, which is a bastion of sound evidence based practice, for some reason, probably because like teachers in red states they actually need to do their jobs properly, and can't just rely on demographics to do all the hard work.