Thanks for the post. If you don't mind, what's your source? It appears to be the published census, and it would be great to have access to it on the web.

People project what they know of Southern culture from the past 145 years and assume it's always applied. Take for example the images taken by Walker Evans in Hale and Perry Counties during 1935-36, later published as Let Us Now Praise Famous Men, 1941. The public believes children in Alabama and other parts of the South have always looked like these. My father grew up in Perry County during the 1930s, so this is a personal issue.
http://www.loc.gov/shop/index.php?action=cCatalog.showSubCategory&cid=65&scid=480&page=0

As your figures indicate, at the time of the Civil War literacy rates were higher in Southern states than they were afterwards. The same is certainly true for standard of living.