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 and academic outcomes." 

The CATO Institute is a free-market think-tank based in Washington, D.C. 

Coulson just released his study, "State Education Trends: Academic Performance and Spending over the Past 40 Years," and he points to this chart that incorporates costs and the number of public school employees with student enrollment and test scores: 

While spending has just about tripled in inflation-adjusted dollars and the number of school employees has almost doubled since 1970, reading, math and science scores for students have remained stagnant. 

"That is remarkably unusual," Coulson wrote in his study. "In virtually every other field, productivity has risen over this period thanks to the adoption of countless technological advances - advances that, in many cases, would seem ideally suited to facilitating learning. And yet, surrounded by this torrent of progress, education has remained anchored to the riverbed, watching the rest of the world rush past it." 

Click for more