The remaining 46 percent of participating students, it found, had either enrolled in private schools as kindergartners or transferred from schools outside of Cleveland.

"The numbers suggest that vouchers in Cleveland are serving more as a subsidy for students already attending private schools than a way for students to leave badly performing public schools," said Zach Schiller, a senior researcher at Policy Matters Ohio, the nonprofit group that did the study. "I don't think national proponents of voucher programs would say the numbers reflect the goal of such a program."

'An Escape Hatch'

The Cleveland voucher program, which was started in the 1996-97 school year, provides up to $2,250 in state money per child to help families pay private school tuition. During the last fiscal year, the state spent $7.7 million on the program, which has 51 participating private schools.

State education officials and supporters of the voucher program said it operates well within its legal obligations. The Ohio law that established the program stipulates that no more than 50 percent of participating students can have been enrolled in private schools before receiving the vouchers.

"The program is meeting its goal of being an escape hatch for parents as they look at the poorly performing Cleveland public schools," said Robert Freedman, a spokesman for the Institute for Justice, a Washington-based legal-advocacy group that represents families participating in the voucher program in their defense of the program against an ongoing federal lawsuit challenging it.

"The majority come from kindergarten, which means parents are able to have an escape hatch when they start their child in school," he continued.

The Cleveland program is the focus of national attention as the U.S. Supreme Court prepares to decide this fall whether to hear an appeal in the case. Opponents of the vouchers argue that they unconstitutionally aid religious schools.

Some voucher opponents said the new study cast even more doubt on the program's constitutionality.

"This study shows that the subsidies are primarily benefiting the parochial schools and the people who are already in them or would have been in them," said Tom Mooney, the president of the Ohio Federation of Teachers. "It calls into question what the taxpayers are paying for here."

State Questions Analysis

State education officials do not dispute the enrollment numbers in the study, which used state data. But they disagree with the way Policy Matters Ohio did the analysis.

Last year, of the 3,741 students in the program, 1,234 had previously attended private schools, and 801 had attended Cleveland public schools, according to the group's study, which breaks out a third category for the other 1,706 students who entered the program in kindergarten or from other geographic areas.

But in its analysis, the state does not break out that third category. So, from its vantage point, the state does not believe the program is disproportionately benefiting private school students.

For example, the state's data for this year show 4,266 students in the voucher program. Of those, 67 percent are technically seen as coming from public schools, and 33 percent were already enrolled in private schools, said Dottie Howe, an Ohio Department of Education spokeswoman.

Policy Matters Ohio, which specializes in economic-policy issues, has board members, including members of labor unions, who oppose vouchers. The organization's funding comes primarily from the George Gund Foundation, a philanthropy based in Cleveland.