Vouchers and graduation rates

The very prolific Jay Greene is out with a new study comparing graduation rates at Milwaukee public high schools with those at voucher schools. The study is described in this article and sponsored by School Choice Wisconsin, which unfortunately does not yet list it on its website. The authors, themselves, seem cautious about their results--and rightly so. They point out that their study does not follow actual students from freshman to graduation; rather it compares the size of the freshman class with that of the graduates.

One problem with the Greene approach is that it apparently makes no adjustment for ninth graders who are repeating that grade (around 30% in Milwaukee). This inflates the denominator of the ratio. In other words, 30% of the students counted as starting the race to graduation one year would have been counted in the previous year.

Another problem is the simplistic model it implies: of a contest between two groups of students, one in public schools, the other in private, to see which will have the most survivors over the next four years. An alternative model is at least as plausible: that many students first try the public schools, later switching to private schools. (I am aware of a private school--not a voucher school--with 27 freshmen and 211 seniors--which would, under the Greene calculation, give it a graduation rate of almost 800%.)

In the alternative model, the voucher schools are more a complement than competition to public schools, particularly valuable in serving students who might otherwise be lost.