SANTA FE, N.M. – For decades, it’s probably the most troublesome question facing education: Why are results for U.S. public school students so mediocre, despite the billions of taxpayer dollars spent? Andrew Coulson thinks he’s got the answer: Because there is no discernible correlation between spending and outcomes. “The takeaway from this study is that what we’ve done over the past 40 years hasn’t worked,” said Coulson, director of the Center For Educational Freedom at the CATO Institute. “The average performance change nationwide has declined 3 percent in mathematical and verbal skills. Moreover, there’s been no relationship, effectively, between spending...