The most startling thing I noticed was how well the West does compared to the East. Aside from the stupid liberal states of California and Hawaii, only one Western state was on the minus side, and that just barely (WY at -0.07).The lack of any discernible pattern underlying the rankings was befuddling. The absence of an obvious demographic explanation lends credence at least to the possiblity that we're getting at the effectiveness (and lack thereof) of what actually goes on throughout the nation's classrooms. It opens up conjecture on what might be taking place (or if we're just hearing a bunch of statistical noise), and ways these thoughts might be tested [Any information on quantifiable measures of the rigor in attaining and maintaining teaching certification, measures of teacher union power by state, and the like would be greatly appreciated!].
Well, Justin's perspicacity is pretty evident in this graphic (brown indicates greater improvement, blue indicates relative deterioration) of the states by relative improvement (in math and reading) from the 2003 class of fourth graders to 2007 eighth graders, for whites only. Excepting California, the West does better than the South and the Northeast, and the differences are stark.
Other commenters are skeptical of the idea that the data reveals anything. It is subject to some noise, with students moving, moving back and forth between public and private schools, an increasing role of heredity in intelligence as students age, and other issues raised in the comments.
But what makes the data remarkable is that the differences are pretty steady over time, at least during the eight year period looked at (and the next task is to peek at other subjects like science and writing as well as look even further back into the nineties to see how well the trends hold up over a longer period of time). We might not be getting a window into teaching effectiveness by state (instead it may be a result of something like different school start times or differing levels in the severity of cheating that is taking place), but we're witnessing something--the 'phenomenon' is not merely the result of randomness.
Regarding the progression as you drive westward, a couple of thoughts come to mind. The US' population center continues to slide to the west (it's now in southeastern Missouri, near the hometown of Rush Limbaugh). A host of IQ measures suggest that the Northeast houses the nation's most intelligent states. As some of these people move into the Midwest and beyond, perhaps they're buoying the performance of the states they arrive in.
Also, unions (presumably those of teachers included) are generally weaker out West. John Stossel targeted New York City due to the strength of the NEA and other teachers unions there in an hour-long special on the dysfunctional state of public education in the US several months ago.