Here's an interesting report on differences in spending by public and private schools by researchers at Rutgers University and Arizona State. A summary says some private schools spend more, some less, than comparable public schools. Some have strong teacher requirements, some don't. Then this:
What's "most striking" about such patterns, Baker observes, is that they are largely explained by religious affiliation alone. Christian Association Schools have the lowest spending, the lowest salaries, teachers with the weakest academic records, and the highest pupil-to-teacher ratios. Moreover, earlier research concludes that these schools have the lowest student test scores. Catholic schools tend to approximate public schools in all these areas. Hebrew schools and independent day schools (generally not religiously affiliated) have higher spending -- often substantially higher -- and this is reflected in these resource categories.
Baker's findings may provide some insights into why research on voucher programs has yielded mixed results regarding student achievement levels for participating low income students. The potentially high-performing parts of the private school sector are the ones that spend much more than available voucher subsidies. In fact, they spend much more than public schools. Private independent day schools -- which have the academically strongest teachers and the smallest classes among private schools -- will, Baker points out, "remain well out of reach of voucher recipients." In many markets, such schools on average spend twice what public schools spend, which in turn is often twice the voucher levels allocated. Thus, even under a voucher scheme that paid what public schools receive per pupil, these private schools would have to subsidize half the total cost of teaching voucher students to match what they spend on their non-voucher students.
Furthermore, even for lower-priced Christian Association Schools and Catholic schools, which are the schools that do often participate in voucher programs, voucher funding levels are likely to provide less money than they need to cover existing costs, raising the schools' financial stress and possibly reducing program quality.
Baker recommends that policy makers who would look to private schools for lessons on how to improve public education begin with a clear awareness of the stark differences among subsets of private schools, avoiding policy recommendations based on averages or isolated instances. He also points to the importance of understanding the differences between private school spending and tuition, given that spending is often subsidized by outside resources (which themselves are often taxpayer subsidized). Regarding voucher policies, policy makers need to understand the tradeoff between attempts to craft policies with a limited impact on the public treasury and to craft policies that provide real choice to voucher recipients. Current policies appear to sacrifice choice for fiscal prudence, but this report demonstrates that the result is access to only a couple parts of the private sector, both of which have strong religious affiliations and neither of which appears to offer academic benefits over public schools.