Andrew Coulson:

Public-school employees have doubled in 40 years while student enrollment has increased by only 8.5%–and academic results have stagnated.
Since 1970, the public school workforce has roughly doubled–to 6.4 million from 3.3 million–and two-thirds of those new hires are teachers or teachers’ aides. Over the same period, enrollment rose by a tepid 8.5%. Employment has thus grown 11 times faster than enrollment. If we returned to the student-to-staff ratio of 1970, American taxpayers would save about $210 billion annually in personnel costs.
Or would they? Stanford economist Eric Hanushek has shown that better-educated students contribute substantially to economic growth. If U.S. students could catch up to the mathematics performance of their Canadian counterparts, he has found, it would add roughly $70 trillion to the U.S. economy over the next 80 years. So if the additional three million public-school employees we’ve hired have helped students learn, the nation may be better off economically.
To find out if that’s true, we can look at the “long-term trends” of 17-year-olds on the federal National Assessment of Educational Progress. These tests, first administered four decades ago, show stagnation in reading and math and a decline in science. Scores for black and Hispanic students have improved somewhat, but the scores of white students (still the majority) are flat overall, and large demographic gaps persist. Graduation rates have also stagnated or fallen. So a doubling in staff size and more than a doubling in cost have done little to improve academic outcomes.