I tend to agree with RA, though the issues are clearly thorny and likely all interrelated.
If you look at per capita income in the southern states, they're uniformly at the bottom of the ranking. SC is #40 in the states, with Louisiana, Alabama, Arkansas, and Mississippi all ranking even lower.
Most school funding comes from property taxes and with a larger impoverish population, those taxes are significantly less per student than in richer counties/areas.
I found
this graph which shows per pupil spending. It shows the southern states as generally spending less per student than northern states.
As opposed to cfdavid, I don't really think all poverty can be ascribed to people wanting to suckle off the public teat. I think the majority of poorer people would jump at the chance to earn $30K-$40K if a job was offered to them. However, those types of jobs are hard to come by without a college degree.