Support for eliminating the cap on how many Milwaukee children can use vouchers to attend private schools is coming from a somewhat unlikely source and for a reason rarely considered.

The source is the Public Policy Forum, a private, non-profit policy research group that generally has taken middle-of-the-road positions on issues and sometimes has butted heads with voucher movement leaders.

And the reason is that eliminating the cap probably won't make much difference.

The heated debate over how to handle the future of the voucher program, now that it has hit the maximum enrollment of about 14,750 allowed by state law, is based in large part on the assumption by almost everyone that without the cap, voucher enrollment will keep growing. Some have speculated that up to 10,000 additional children in the city could end up in state-supported private and religious schools over the next few years.

But in its annual analysis of trends in the precedent-setting voucher program, the Public Policy Forum says that the growth in total participation in the program has slowed after years of rapid increases. Even without a cap, the total enrollment may not grow much more from current levels, the report says.

"The data trends suggest that lifting the cap would not result in large numbers of new students joining the program," the report says. "So why not lift the cap? Keeping the cap in place only creates a false sense of demand; removing it would more accurately demonstrate the program's level of success in the marketplace."

Annaliese M. Dickman, the forum's research director, added in an interview that the cap - equal to 15% of enrollment in Milwaukee Public Schools - was created originally as a political compromise and there was no policy argument or practical reason for setting it at 15% or any other level.

She said the number of students on vouchers grew 2.8% from last year to this year, by far the smallest annual percentage increase in voucher students since the Wisconsin Supreme Court approved expanding the program and including religious schools in June 1998.

Key leaders of the school choice movement believe that there would be substantial expansion of the program if the cap were lifted, and Department of Public Instruction officials said they expect a significant number of new schools to apply to join the program for next fall. Currently, more than 120 schools have students whose education is paid for by publicly funded vouchers of up to $6,351 per student.

The forum's report also described several other trends in the voucher program:

• Student turnover remains high from year to year. The report says 28% of students who were on vouchers in September 2004 had left the program by September 2005, not including those who graduated from high school.

• High school enrollment declined from last year to this year. Dickman said the forced closing of one large voucher school, Academic Solutions, in January 2005, was one cause, but she suggested another factor was that serving high school students is more expensive than serving grade school students while voucher payments remain the same regardless of grade.

• More than 90% of the schools in the program give standardized tests, with about 40% giving the tests used by public schools statewide or very similar tests from the same testing company.