The Washington Post reports on results of a study of performance by students in the only federally funded school voucher program, in Washington, D.C.

D.C. students who use vouchers to attend private schools perform significantly worse in math than their public school peers, according to a federal study that could cast a cloud over Education Secretary Betsy DeVos’s quest to expand voucher programs across the country.

This week’s study from the Institute of Education Sciences, part of the U.S. Education Department, found that math scores were 10 percentage points lower for students who used vouchers compared with students who applied for the scholarship program but were not selected through a lottery. The students who were not chosen for the voucher program typically attend public schools in low-income neighborhoods.

Reading scores for voucher students were also lower, though the difference was not statistically significant.

This follows a 2017 study that found voucher students performed worse a year after moving to private schools.