The story behind the Milwaukee school choice study: The results are more complicated than they are sometimes portrayed.

John F. Witte and Patrick J. Wolf:

The past few weeks have seen a lively debate surrounding the Milwaukee Parental Choice Program and Gov. Scott Walker’s various proposals to expand it. It is time for researchers to weigh in.
For the past five years, as mandated by state law, we have led a national team in a comprehensive evaluation of the choice program. Our study has applied social science research methods to carefully matched sets of students in the choice program and in Milwaukee Public Schools. Whenever possible, we have used measures that are applied consistently in the public- and private-school sectors, generating true apples-to-apples comparisons.
This is what we have learned:
Competitive pressure from the voucher program has produced modest achievement gains in MPS.
The three-year achievement gains of choice students have been comparable to those of our matched sample of MPS students. The choice students are not showing achievement benefits beyond those of the students left behind in MPS.
High school students in the choice program both graduate and enroll in four-year colleges at a higher rate than do similar students in MPS. Being in the choice program in ninth grade increases by four to seven percentage points a student’s prospects of both graduating from high school and enrolling in college. Students who remain in the choice program for their entire four years of high school graduate at a rate of 94%, compared with 75% for similar MPS students.