President Obama said last month that America can educate its way to prosperity if Congress sends money to states to prevent public school layoffs and "rehire even more teachers." Mitt Romney was having none of it, invoking "the message of Wisconsin" and arguing that the solution to our economic woes is to cut the size of government and shift resources to the private sector. Mr. Romney later stated that he wasn't calling for a reduction in the teacher force—but perhaps there would be some wisdom in doing just that.

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.

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.

Nor can the explosive growth in public-school hiring be attributed to federal spending on special education. According to the latest Census Bureau data, special ed teachers make up barely 5% of the K-12 work force.