WASHINGTON (AP) — Students attending private schools in the nation's capital through a federally funded voucher program are doing worse in math compared to their peers, according to a government study released Thursday.

The findings added fuel to one of the most heated debates in the education community: whether taxpayer money should be used to pay for private schools. Critics jumped on the study to reiterate that vouchers don't work. Proponents stressed that test scores are not the only way to measure school quality.

The study, conducted by the Education Department's Institute of Education Sciences, looked at students who enrolled in the program in the years 2012-2014 and compared them to their peers who applied for the vouchers through a lottery, but were not selected. The study evaluated students one year into their study,

The analysis revealed that students who attended private schools with voucher money scored 7.3 percentage points lower in math compared to those students who didn't get in. The study did not find any statistically significant differences in reading skills.

But among students who had attended low-performing schools, the key targets of the voucher program, the study did not reveal any significant change in either math or reading.

At the same time, the program positively affected perceptions of school safety. Some 72 percent of parents in the program ranked their school as very safe, compared to 56 percent among those parents whose children didn't get into the program.

Rep. Bobby Scott, D-Va., said the findings are proof that voucher programs don't help students and waste public resources.

"D.C. students using vouchers actually lose learning; they performed significantly worse on math in the first year they used the voucher," Scott said in a statement. "We know that these failed programs drain public schools of limited resources, only to deliver broken promises of academic success to parents and students."

Education Secretary Betsy DeVos, who has spent more than two decades advocating for charter and private schools, said the one-year study was not enough to make long-term conclusions about school choice programs. She also said that offering parents choices benefited the whole system.

"When school choice policies are fully implemented, there should not be differences in achievement among the various types of schools," DeVos said in a statement. "D.C.'s traditional public schools have not suffered as a result of being part of a system that allows choice; rather, they have greatly improved."

The District of Columbia Opportunity Scholarship Program was created by Congress in 2004 and was reauthorized in 2011. It currently serves more than 1,100 mostly low-income students. Families get up to $8,400 for elementary and up to $12,600 for high school students.

Lindsey Burke, director of education policy studies at the conservative Heritage Foundation said the results can be explained by the fact that public schools in the district may have improved because of competition inserted into the system by vouchers. She also cited a previous iteration of this study, which showed that using the voucher increased the graduation rate by 21 percentage points.

Samuel Abrams, director of the National Center for the Study of Privatization in Education at Teachers College, Columbia University, said voucher programs have not proven to improve academic results.

"They provided choice, which is itself an objective for many parents, but they have not generated the academic outcomes that advocates and parents have expected," Abrams said.

He added that merely putting low-income students into private schools while they continue to live in unsafe, high-need neighborhoods will not solve the problem and that more needs to be done to bridge income inequality and improve access to health care and early childhood education.