Perhaps the president and other Democrats oppose vouchers because they fear—as the president's remarks in Ireland suggest—that religious schooling undermines social cohesion. The belief that religious schools erode civic goals has a long history. In the mid-19th century, religious schools, Catholic schools in particular, were accused of reinforcing separate identities rather than shared American values. Much has changed in education since then, but a suspicion lingers in some quarters that church-operated schools breed intolerance.
Yet this view has been contradicted by a growing body of social-science evidence. In a review of the research, my colleague Patrick Wolf identified 21 studies of the effect that public and private schooling have on political tolerance. Tolerance is typically measured by asking students to name their least-liked group and then determining whether students would allow members of that group to engage in political activities, such as running for elected office or holding a rally. The more willing students are to let members of their least-liked group engage in these activities, the more tolerant they are judged to be.
I conducted two of those 21 studies, and others were produced by researchers at institutions including Harvard, Notre Dame and the University of Chicago. The studies varied in whether they looked at national or local samples of students and whether they examined secular, religious or all types of private schools. Of those studies, only one—focusing on the relatively small sector of non-Catholic religious schools—found that public-school students are more tolerant. Eleven studies, examining both secular and religious private schools, found that private-school students are significantly more likely to be tolerant, and nine found no difference.