Researchers Christopher Lubienski and Joel Malin note that a growing number of states have adopted voucher plans on the assumption that vouchers will “help poor kids escape failing public schools,” but the reality is that a substantial body of evidence finds that vouchers actually harm student academic performance.

After two decades of choice advocates arguing that school vouchers in particular improve academic achievement for poor children, Trump elevated Betsy DeVos, one of the leading voucher proponents, as his secretary of Education. State policymakers have also massively scaled-up school vouchers and voucher-like programs such as education savings account programs across the country. However, over the last four years, researchers have consistently found insignificant or, more often, substantially negative impacts on learning for the children whose parents have enrolled them in these programs. Such negative impacts are largely unprecedented in evaluations of educational interventions, raising questions about the ethics of experimenting on children through these programs.

When plans to use taxpayer funds for private schooling were first introduced into American education in the early 1990s, they were pitched as a way to give poor and urban children a chance to leave failing public schools for better learning opportunities in what were thought to be more effective private schools.

Indeed, there are reasons to expect school vouchers would work, such as the facts that choosing a school might allow for better matching between a child’s preferred learning style and a school’s educational program, or that private schools tend to have smaller classes.

But it has never been clear that using vouchers to choose private schools leads to better educational outcomes for students.

When vouchers were first studied, researchers fought vicious battles over relatively minor differences in academic achievement. Voucher advocates like DeVos embraced any evidence of learning gains for students using vouchers to switch to private schools, and a number of think tanks and large philanthropies like the Walton Family Foundation also lined up to support this education reform. Some even saw vouchers as the key for reducing achievement gaps between white and minority students. But while most researchers found that any gains were rather negligible overall, advocates argued that vouchers were at least not harming students’ academic achievement.

Recently though, there has been a sea-change in the results.

As city-based pilot programs in places like Cleveland and Milwaukee were eclipsed by statewide programs in Ohio, Indiana, Louisiana, and elsewhere, researchers are consistently seeing large, significant, negative impacts — outcomes almost unheard of in evaluations of education interventions.

Studies have converged on the failure of vouchers. Parents may be satisfied, but their children are not learning more.

For instance, research on Louisiana’s program indicates that when some children performing squarely in the average range use a voucher to enroll in a private school, their scores fall almost to the lowest performing quartile of students overall. And initial hopes that those losses were temporary have not panned out.

Stated simply, students using vouchers to attend private schools are falling behind their peers in learning. That is, DeVos and her allies are promoting programs that hurt children.

Do no harm might be a good guideline for school interventions. If it were, all the voucher programs enacted in the past 30 years would be canceled.