The Economist has an article about the benefits about parental choice in education:
Voucher schemes are running in several different countries without ill-effects for social cohesion; those that use a lottery to hand out vouchers offer proof that recipients get a better education than those that do not.
The article cites studies of choice-based programs in Sweden, Colombia, and the U.S.
One argument that has been raised against tuition tax credits in MIssouri is that choice leaves disadvantaged children behind or doesn't work for everyone. These studies of voucher programs prove this wrong. Choice works in different places and different circumstances. Public schools, on the other hand, often work well for children who live in affluent neighborhoods but fail children in inner cities--like in Saint Louis.