Supporters of school voucher programs are excited over a new study that’s supposed to show that students attending private schools in the Milwaukee program graduate at a much higher rate than students in the city’s public schools. About 64% of the students who start high school using vouchers at ten private schools graduated four years later compared to only 36% of the students in the public schools.

Miracle? Not necessarily when you look a little deeper. For one thing the study focused on only 10 of the 100 schools in Milwaukee that accepts voucher students. Why didn’t the researchers include all 100 schools? And, as always, you must take into consideration who paid for the study. In this case it was School Choice Wisconsin, a group formed last April as an advocate for school voucher programs in the state. Both points would drain a lot of credibility from this research.

The author of the study does, however, make a very good point about vouchers.

"Nationwide, roughly half of students in urban high schools fail to receive a regular high school diploma," said Greene, a political scientist and senior fellow at the Manhattan Institute for Policy Research, a conservative organization based in New York. "In Milwaukee and Cleveland, it’s well under half. Any program that offers a big improvement in the probability of urban students graduating is something that we should be very interested in."

And so does another researcher studying voucher programs.

Richard D. Kahlenberg, a senior fellow at the Century Foundation, a policy group based in the District, said the report "leaves unanswered the most important question: What is the effect of the voucher program on the large number of students left behind in the regular public schools?"

"It’s hardly surprising that a very small number of students from families motivated enough to apply to a voucher program do well when placed in a private school environment — one where students are surrounded by a community of highly motivated peers and their tuition-paying parents," he said.

The debate continues.