Much is uncertain about the total effects of a broad voucher program on education. The United States has relatively limited experience with choice in general and vouchers in particular, and that experience has occurred in rather narrowly prescribed experiments. It is therefore difficult to project the results of a broader voucher program by simply expanding on past experience with such a program. On the other hand, considerable experience relates to various aspects of schools that have been highlighted as potentially important. This chapter concentrates on one such area—the role of school peers—and describes what related research has to say about this potential avenue of voucher effects.