Alan Borsuk:

The number of Milwaukee children attending private schools using publicly funded vouchers has crossed 20,000 for the first time, according to data released by the Wisconsin Department of Public Instruction.
At the same time, the number of students in the main roster of Milwaukee Public Schools elementary, middle and high schools has fallen below 80,000 for the first time in well over a decade and declined for at least the 10th year in a row.
Amid a host of other factors shaping the school landscape in Milwaukee, those two trends point to some of the key stresses and looming issues for both MPS, which remains one of the nation’s larger school systems, and the voucher program, the largest, oldest and arguably most significant urban school voucher program in the United States.
For MPS, declining enrollment means greater financial pressure, a need to close school buildings and a continual search for ways to attract students and raise overall levels of achievement.
For the voucher program, the increase means the state-imposed cap on its size is coming into view, and issues related to the property-tax impact of the funding program are becoming more urgent. In addition, with Democrats having gained control of the state Legislature, efforts to impose more regulations on schools with voucher students are likely to become much more serious.
Nationwide, the momentum behind support for voucher programs such as the one in Milwaukee has been limited, and most likely has lost further steam with the election of Sen. Barack Obama to be president. Although Obama favors charter schools – generally, independent publicly funded schools that have more public accountability than private schools – he has not favored vouchers, and the Congress, controlled firmly by Democrats, is not going to support such plans either.

Somewhat related: A Madison School District enrollment analysis discloses an increase in outbound open enrollment.