In Short

Recent studies purport to show that voucher programs result in better achievement by black students at private schools, and that vouchers motivate public schools to improve. Those results are overstated, a new analysis argues.

Martin Carnoy, a Stanford University education and economics professor, reviewed two voucher studies for the Economic Policy Institute, a labor-backed think tank.

The first study involved recipients of privately funded vouchers in New York City, the District of Columbia, and Dayton, Ohio. Paul E. Peterson, a prominent voucher researcher and a professor of government at Harvard University, found last year that black students using the vouchers outperformed a control group made up of students who had applied for vouchers but...