(This is an update of a post I originally wrote on August 21. I’ve included the new DC voucher findings.)
Here is what I believe is a complete (no cherry-picking) list of analyses taking advantage of random-assignment experiments of the effect of vouchers on participants. As I’ve previously written, 9 of the 10 analyses show significant, positive effects for at least some subgroups of students.
All of them have been published in peer reviewed journals or were subject to outside peer review by the federal government.
Four of the 10 studies are independent replications of earlier analyses. Cowen replicates Greene, 2001. Rouse replicates Greene, Peterson, and Du. Barnard, et al replicate Peterson and Howell. And Krueger and Zhu also replicate Peterson and Howell. All of these independent replications (except for Krueger and Zhu) confirm the basic findings of the original analyses by also finding positive effects.
Anyone interested in a more complete discussion of these 10 analyses and why it is important to focus on the random-assignment studies, should read Patrick Wolf’s article in the BYU Law Review that has been reproduced here.
These 6 studies conclude that all groups of student participants experienced reading or math achievement gains and/or increased likelihood of graduating from high school as a result of vouchers:
Howell, William G., Patrick J. Wolf, David E. Campbell, and Paul E. Peterson. 2002. “School Vouchers and Academic Performance: Results from Three Randomized Field Trials.” Journal of Policy Analysis and Management, 21, April, pp. 191-217. (Washington, DC: Gains for all participants, almost all were African Americans)
Wolf, Patrick, Babette Gutmann, Michael Puma, Brian Kisida, Lou Rizzo, Nada Eissa, and Marsha Silverberg. March 2009. Evaluation of the DC Opportunity Scholarship Program: Impacts After Three Years. U.S. Department of Education, Institute of Education Sciences. Washington, DC: U.S. Government Printing Office. (In the fourth year report the sample size shrunk so that the positive achievement effect barely missed meeting a strict threshold for statistical significance — p < .06 just missing the bar of p < .05. But this new report was able for the first time to measure the effect of vouchers on the likelihood that students would graduate high school. As it turns out, vouchers significantly boosted high school graduation rates. As Paul Peterson points out, this suggests that vouchers boosted both achievement and graduation rates in the 4th year. Read the 4th year evaluation here.)
These 3 studies conclude that at least one important sub-group of student participants experienced achievement gains from the voucher and no subgroup of students was harmed:
Barnard, John, Constantine E. Frangakis, Jennifer L. Hill, and Donald B. Rubin. 2003. “Principal Stratification Approach to Broken Randomized Experiments: A Case Study of School Choice Vouchers in New York City,” Journal of the American Statistical Association 98 (462):299–323. (Gains for African Americans)
Howell, William G., Patrick J. Wolf, David E. Campbell, and Paul E. Peterson. 2002. “School Vouchers and Academic Performance: Results from Three Randomized Field Trials.” Journal of Policy Analysis and Management, 21, April, pp. 191-217. (Dayton, Ohio: Gains for African Americans)
Peterson, Paul E., and William G. Howell. 2004. “Efficiency, Bias, and Classification Schemes: A Response to Alan B. Krueger and Pei Zhu.” American Behavioral Scientist, 47(5): 699-717. (New York City: Gains for African Americans)
This 1 study concludes that no sub-group of student participants experienced achievement gains from the voucher:
(Update: For a review of systemic effect research — how expanded competition affects achievement in traditional public schools — see here.)