Educational attainment for rural MS whites shouldn't be any worse than for rural Whites in AL/GA. The fact that the uber-White Mississippi counties stick out on that map compared to AL/GA has something to do with whatever racial turnout dynamics you're using.
^^^ And FWIW, Mississippi whites in 2012 statewide in my calcs were one shade lighter/less Democratic than AL whites (another big topic I've covered in the past is how the AL exit polls in 2008 had to be wrong by a considerable sum, underestimating white D support): 16% versus 11%. That's enough to essentially explain the difference in shading between MS & AL rural counties in 2012, and when comparing to GA, again, I believe that GA having more/smaller counties and more small cities as a result produces a slightly (~5%) more Democratic rural landscape than in MS.
I know MS looks weird on the map, but to me, it makes sense. There are other places where the map abruptly cuts (between GA/NC, for example, which is definitely accurate; along the 35th parallel in general across the eastern US, etc) but are nevertheless not the result of flawed modeling.
I was wrong about the rural educational levels, though - at least when basing it off of jimrtex's UCC delineations and the data from 2015. I might argue that there is some skewing here (again, because it uses county-level data and Mississippi's counties are geographically larger/a much greater % of the population in MS falls into the "rural" category), but alas:
AREA POP COLLEGE %
GA-Rural 2669107 548545 20.6%
GA-Urban 7530893 3011255 40.0%
GA-State 10.200 m 3559800 34.9%
MS-Rural 1835885 442656 24.1%
MS-Urban 1148115 401816 35.0%
MS-State 2.984m 844472 28.3%
Probably caused by greater Athens being urban while Lafayette and Oktibehha are rural
