There are many good reasons to oppose a federal school voucher program, but a supposed lack of evidence that school choice improves student outcomes isn’t one of them. Sadly, Sen. Patty Murray (D‑WA), the ranking minority member of the U.S. Senate’s education committee, repeated this canard during the debates over a proposed amendment that would have added a federal school voucher program to the No Child Left Behind replacement bill:

What’s more, studies of voucher programs in Milwaukee and the District of Columbia have shown that they do not improve students’ academic achievements, she said. “Study after study has shown that vouchers do not pay off for students or taxpayers,” Murray said. 

That’s simply not true. According to Dr. Patrick Wolf, coauthor of the only longitudinal study of the effect of Milwaukee’s voucher program, “school choice in Milwaukee has had a modest but clearly positive effect on student outcomes.”

First, students participating in the Milwaukee Parental Choice (“voucher”) Program graduated from high school and both enrolled and persisted in four-year colleges at rates that were four to seven percentage points higher than a carefully matched set of students in Milwaukee Public Schools. Using the most conservative 4% voucher advantage from our study, that means that the 801 students in ninth grade in the voucher program in 2006 included 32 extra graduates who wouldn’t have completed high school and gone to college if they had instead been required to attend MPS.

Second, the addition of a high-stakes accountability testing requirement to the voucher program in 2010 resulted in a solid increase in voucher student test scores, leaving the voucher students with significantly higher achievement gains in reading than their matched MPS peers.

In the final year of the study, Milwaukee voucher students in grades 3–9 performed about 15 percent of a standard deviation higher on standardized reading tests, “a modest but meaningful educational difference.” Moreover, the study concluded that Milwaukee district-school students were “performing at somewhat higher levels as a result of competitive pressure from the school voucher program.” And contrary to Sen. Murray’s assertion that “vouchers do not pay off for taxpayers,” the study found that the voucher program saved the state nearly $52 million in fiscal year 2011 because the vouchers were worth about half of the cost per-pupil at the district schools.

Wolf also studied the effects of Washington, D.C.‘s voucher program under the auspices of the U.S. Department of Education. The study found that students offered vouchers graduated high school at a rate 12 percentage points higher than the control group, 82 percent to 70 percent respectively. In a follow-up study, Wolf and his team determined that the voucher program was a boon to taxpayers as well:

The District of Columbia Opportunity Scholarship Program (OSP) produced $2.62 in benefits for every dollar spent on it. In other words, the return on public investment for the private-school voucher program during its early years was 162 percent. 

In total, there have been a dozen random-assignment studies–the gold standard of social science research–by researchers at Harvard, Princeton, the University of Chicago, the Brookings Institution, and elsewhere examining the impact of private school choice programs. Of those, 11 found modest but statistically significant positive impacts on student performance, including improved test scores and higher rates of high school graduation and college enrollment. One found no statistically discernible difference and none found any harm. For Sen. Murray’s benefit, here is a sampling:

• Joshua M. Cowen, “School Choice as a Latent Variable: Estimating ‘Complier Average Causal Effect’ of Vouchers in Charlotte,” Policy Studies Journal, May 2008. – After one year, voucher students had reading scores 8 percentile points higher than the control group and math scores 7 points higher.

• William G. Howell and Paul E. Peterson, The Education Gap: Vouchers and Urban Schools, Brookings Institution, 2002, revised 2006. – After two years, African-American voucher students had combined reading and math scores 6.5 percentile points higher than the control group.

• Jay P. Greene, “Vouchers in Charlotte,” Education Next, Summer 2001. – After one year, voucher students had combined reading and math scores 6 percentile points higher than the control group.

• Cecilia E. Rouse, “Private School Vouchers and Student Achievement: An Evaluation of the Milwaukee Parental Choice Program,” Quarterly Journal of Economics, May 1998. – After four years, voucher students had math scores 8 NCE points higher than the control group. NCE points are similar to percentile points.

In recent years, left-wing politicians and organizations have repeatedly closed their eyes and plugged their ears with regard to the copious evidence that school choice works. But ignoring the evidence doesn’t make it go away.