On a whim, I decided to compare school performance data with other measurable characteristics.
I chose two sets of achievement data: the Education Week Quality Counts State Report Cards Map (K-12 achievement), and the Nation’s Report Card for 8th grade reading and math.
I looked for correlation with multiple data sets: state-by-state rankings of charter school laws from a pro-charter perspective (source), state-by-state union strength rankings from a conservative think tank (source), per-student expenditures in each state according to the NEA (source; look for table H-11), percentage of people in each state who identify as Democrats (since people often blame educational dysfunction on Democrats)(source); and finally, median income per state according to the U.S. Census (source).
Median income had the strongest correlation with test scores, with r values of 0.5 and 0.38. The other factors had no appreciable correlation at all.
If you’d rather not scroll around in the little embed window above, here’s a direct link to the spreadsheet.