This and the other work from the National Education Policy Center seems to be very strong and balanced, with very informative reviews
In this case it reaches a clear conclusion that the author of the study reviewed did prove his point that competition works.
Review of A Win-Win Solution: The Empirical Evidence on How Vouchers Affect Public Schools, Nat. Ed. Policy Center
A Win-Win Solution: The Empirical Evidence on How Vouchers Affect Public SchoolsAdvocates of vouchers argue that nearby public schools will be forced to compete for students, leading to improvements for voucher users and non-users alike. Critics worry that the students who use vouchers to leave public schools will have parents with higher levels of education and be less expensive to educate, and that losing these students will cause those schools to enter spirals of decline. This new report purports to gather all available empirical evidence on the question of the competitive effects of vouchers, finding a strong consensus that vouchers help public schools. But the report, based on a review of 17 studies, selectively reads the evidence in some of those studies, the majority of which were produced by voucher advocacy organizations. Moreover, the report can’t decide whether or not to acknowledge the impact of factors other than vouchers on public schools. It attempts to show that public school gains were caused by the presence of vouchers alone, but then argues that the lack of overall gains for districts with vouchers should be ignored because too many other factors are at play. In truth, existing research provides little reliable information about the competitive effects of vouchers, and this report does little to help answer the question.