There is an interesting new study out: the Cardus Education Survey. It compares the effect of private (Protestant, Catholic, and Non-Religious), public schools and home-schooling.
Christianity Today's summary is in the Sept 2011 issue on page 11.
http://www.christianitytoday.com/ct/special/pdf/110829spot_lastingschool.pdf
The full 56 page CES Phase I report is at:
http://www.cardus.ca/research/education/
I haven't read the full report.