The heated national debate about whether families should get public money to send their kids to private schools is full of big questions.

Do vouchers raise test scores or lower them? Do they help or hurt students over the long term? Do they damage public schools or push them to improve?

Chalkbeat combed through some of the most rigorous academic studies to get the answers.

Two caveats before we begin: First, context matters. Researchers look at specific programs at certain times with their own sets of rules. New initiatives — like a dramatic expansion of private school choice programs of the sort the Trump administration once promised — could mean entering uncharted waters, where past research becomes a less reliable guide.

Second, the voucher debate is often based on values. Research studies can’t answer philosophical questions on whether public money should go to religious schools or if providing more choices for parents is an inherent good.

With that in mind, here’s what you should know:

Recent studies suggest that vouchers lower student test scores, especially in math.

In the last few years, a spate of studies have shown that voucher programs in IndianaLouisianaOhio, and Washington D.C. hurt student achievement — often causing moderate to large declines.

Advocates have pushed back, saying the programs were new and results might improve over time. That generally hasn’t happened though, at least in math.

“While the early research was somewhat mixed … it is striking how consistent these recent results are,” said Joe Waddington, a University of Kentucky professor who has studied Indiana’s voucher program. “We’ve started to see persistent negative effects of receiving a voucher on student math achievement.”

In Louisiana, after two years in the program, a student who started at the 53rd percentile dropped to the 37th percentile in math. By and large, those negative effects persisted through year four, particularly in math and science.

In D.C., students using a voucher saw scores fall 10 percentile points in math and about 4 points in reading after two years, compared to students who applied for a voucher but didn’t get one.

In Indiana, students in the program saw initial dips in math that persisted for four years. (An earlier version of the same study found evidence of a bounce back among students who remained in private schools.)

The Ohio study showed that even three years into the program, the negative impacts of using a private school voucher persisted.

Older studies tended to show neutral or modest positive effects of vouchers on academic performance, and until recently, few if any studies had shown that vouchers actually led to lower achievement among students who received them. It’s not clear what has changed, but one theory is that public schools have improved — or at least gotten better at raising test scores — in response to accountability measures like No Child Left Behind.

PHOTO: Dylan Peers McCoy
Students sewing during a class at the School for Community Learning, a progressive Indianapolis private school that depends on vouchers.

Studies show that vouchers have a neutral or positive impact on student outcomes later in life, like attending college or graduating high school.

Some supporters of vouchers downplay the recent studies by pointing to research on the longer-run effects of the programs. Here the research is somewhat more positive, but the studies are also limited and generally older. In each case, the researchers looked at students who entered voucher programs many years ago — a necessary trade-off when examining long-term outcomes.

A study of Milwaukee’s long-running voucher program found that participants were more likely to graduate high school and attend four-year colleges. A recent follow-up study confirmed these results, but found that vouchers had no statistically significant effect on students’ likelihood of actually completing college.

A 2010 federal analysis of the D.C. voucher program found that its students were 21 percentage points more likely to complete high school (according to a survey of their parents, not a direct measure of graduation). But a 2018 follow-up analysis found that voucher recipients were no more likely to enroll in college.

A private school scholarship program in New York did not lead to improvements in college enrollment on average, but did seem to have a positive effect for black and Hispanic students specifically. In Florida, a 2017 study and 2019 follow-up found that its tax credit program, the largest private school choice initiative in the country, led to increases in college enrollment and degree completion. Specifically, 12 percent of students who went to a private high school using a tax credit earned a bachelor’s degree; that compares to 10 percent among demographically similar students in public schools.

It remains an open question whether the more recent initiatives can expect those results. The four programs weren’t hurting test scores in the short term; all had positive or no effects on scores.

study of Louisiana’s program — the one that initially showed big declines in test scores for elementary and middle school students — found that it did not have any clear effect on college enrollment among older students.

Research suggest that vouchers or tax credit programs lead to some test score gains in public schools.

There is a large body of evidence suggesting that public schools improve in response to competition from school voucher or tax credit programs, at least as measured by test scores.

This has been seen in studies of Florida, Louisiana, Milwaukee, Ohio, San Antonio, and even Canada. As a recent research overview put it, “Evidence on both small-scale and large-scale programs suggests that competition induced by vouchers leads public schools to improve.”

The impact, though, is often fairly small and can dissipate over time. There do not appear to be any studies on the effect of voucher competition on measures other than test scores.

PHOTO: U.S. Department of Education

Attending a private school may improve parent satisfaction, particularly when it comes to school safety.

Families tend to be more satisfied with private schools, though it’s not clear why.

The older D.C. study showed that families who received vouchers had higher rates of parent (but not student) satisfaction. The latest D.C. analysis showed parents and students perceived private schools as substantially safer; parents also seemed more satisfied with them overall, though these results weren’t statistically significant.

An older report by the Manhattan Institute, a conservative think tank, found that families of students with disabilities using a voucher in Florida were dramatically more satisfied with the new private school than their previous public school. A recent analysis of national data showed that private-school parents were also more satisfied than those sending their children to public schools — though it could not establish cause and effect.

We know very little about how tax credit tuition programs affect students who participate.

Despite their expansion in recent years, tax credit programs — which use generous tax breaks to incentivize donations to organizations that then offer private school scholarships — have rarely been studied.

These programs are similar to school vouchers, in that they redirect taxpayer dollars to private schools, but they tend to be significantly less regulated. For instance, they usually do not require participating private schools to take state tests or, in some cases, any standardized tests at all. That’s part of why there’s so little research on how using one of those scholarships affects students.

The only program that has been rigorously studied, Florida’s tax credit scholarship, had either no effect or small positive effects on student test scores. But that was only prior to 2010; since then, changes to testing requirements have made direct comparisons to public school students impossible. More recent studies looking at students who entered the program between 2004 and 2011 found that it boosted college attendance and completion.

Voucher programs targeted at low-income students are not likely to increase segregation — but a larger-scale program might.

There is surprisingly little research on the effects of private school choice programs on segregation. Existing studies have not found evidence that voucher programs targeted at low-income students worsen segregation. A recent study in Louisiana pointed to positive effects of vouchers on integration, while an older analysis of Milwaukee showed no impact.

However — based on research in other countries and other school choice initiatives including charter schools — there is reason to worry that a large-scale voucher program open to families regardless of income would exacerbate segregation. Prominent school choice advocates generally back a dramatic expansion of this sort.