* Read the executive summary. Half of the subgroups did not have improved performance. Math performance did not improve. Reading scores did improve, but this specific improvement cannot be meaningfully be attributed to the public vs. private nature of the schools. And, the study does attempt to figure out if the reading improvements could be replicated within the public school system by copying the reading programs used in the private schools.

* In the third year, over 83% of the participating students were attending schools where they were forced to endure continuous daily religious indoctrination. This is completely unethical.

* No attempt was made to measure the performance of students that attended a school designed for religious indoctrination against the students who attended a school designed expressly for education.

* According to the study, many parents (19%) turned down the vouchers they received after their students were accepted to public charter schools. It seems like parents are showing a strong preference for charter schools over private schools. IMO, this warrants further investigation into the funding of public charter schools instead of public funding of private education.

* According to the study, many parents of special needs students were not able to use their vouchers because the private schools were not able to provide the necessary services. The public schools are bearing nearly all of the costs of caring for special needs students whereas private schools are mostly punting on the issue. Similarly, if you get kicked out of a public or private school for behavioral or criminal reasons then you will be sent to a public alternative high school. Cost comparisons need to be made using comparable student populations.

* All measurements in this study suffer heavily from selection bias. Much of the data comes from voluntary surveys that were filled out by parents. It was basically a competition between political groups to convince the most parents on their side to return the surveys. Parents and students who were not interested in their students' education and/or the political ramifications of the survey are likely severely under-represented.

It is silly to draw conclusions about the effectiveness of private schools vs. the effectiveness of public schools by Cato's summary or my summary of the study. A summary of a summary of a study can be easily spun however the writer wants to spin it. AFAICT, the study report itself has very little actionable information in it; at best, it points out areas that need more study before any conclusions can be drawn.