Bill Lueders:

“School choice” is a broad term that refers to a wide range of alternatives, including themed charter schools that are entirely under the control of their home school districts. Forty states and the District of Columbia have those in place, according to the American Federation for Children, a national school choice advocacy group.
But it is the voucher programs, in which public funds are used to send children to private schools, that are the focus of much of the energy around the choice movement. Seven states and the District of Columbia have those, and Milwaukee’s voucher program is the first and largest of its kind in the country. That makes Wisconsin a key national battleground.
“Wisconsin has a high level of value to the movement as a whole,” says Robert Enlow, president of the Indianapolis-based Friedman Foundation for Educational Choice, a nonprofit group that advocates for school choice. The state, he says, is notable for “the high level of scholarship amounts that families can get.”
Milwaukee’s voucher program had 20,300 full-time equivalent voucher students at 102 private schools in 2010-11, compared to about 80,000 students at Milwaukee’s public K-12 schools. The total cost, at $6,442 per voucher student, was $130.8 million, of which about $90 million came from the state and the rest from the Milwaukee Public Schools.
Critics see the school choice program as part of a larger strategy — driven into high gear in Wisconsin by the fall election of Gov. Scott Walker and other Republicans — to eviscerate, for ideological and religious reasons, public schools and the unions that represent teachers.

It would be interesting to compare special interest spending in support of the status quo, vs groups advocating change, as outlined in Bill Lueders’ article. A few links: