From the article:
Southern states Mississippi, Alabama and Louisiana are among the weakest performers, with results similar to developing countries such as Kazakhstan and Thailand.
Yeah, I teach math at a large university in the deep south, and this doesn't surprise me at all. Students are unprepared for college math classes, and I see a lot of behavior that I wouldn't have expected in a math class. For example, I always have students that try to memorize their way through class, mostly in calculus 1. They don't practice any problems, they don't try to understand the material, but they've got flash cards and highlighted notes and sticky tabs out the wazoo.
It's like they all had a bunch of "study skills" drilled into them in high school and no one ever bothered to explain that these are supposed to aid actually understanding the material. They're so used to just regurgitating things onto tests that I guess a lot of them really do think memorizing is understanding.
Now I realize the following is just anecdotal, but I know several people who teach high school math throughout the deep south, and all of them say the same thing: they aren't really allowed to teach. School administrators have a death grip on teachers' jobs. Teachers are told what, when, and how to teach the material. They're basically reading scripts. And of course they're all teaching to the state end of course tests too, probably because those are used to measure administrators' performances.