For report NCEE 2010-4018 Evaluation of the DC Opportunity Scholarship Program http://ies.ed.gov/ncee/pubs/20104018/index.asp.

The DC Opportunity Scholarship Program is the first federally funded voucher program in the United States. A congressionally-mandated evaluation of the effectiveness of the program was conducted with two cohorts of applicants (spring 2004 and spring 2005) who entered lotteries to determine whether they would receive a private school scholarship. These approximately 23000 students were administered academic assessments and they and their parents, along with DC public and private school principals, were surveyed over four years about their experiences. These data were released along with the final report (http://ies.ed.gov/ncee/pubs/20104018/index.asp).