Looking inside the Black Box: What School Factors Explain Voucher Gains in Washington, D.C.?

Recently, a number of evaluations of private school voucher programs in the United States have reported achievement gains for voucher users, especially African Americans. These studies tend to be structured as Randomized Field Trials (RFTs), where participants are assigned to treatment (offered a voucher) and control (not offered a voucher) groups by lottery. A major advantage of RFTs is that the randomization process controls for a number of factors, measurable and unmeasurable, that otherwise might confound the assessment of voucher effects. A major shortcoming of RFTs is that they tend to be black-box evaluations that inform policy analysts little about why or how a policy intervention yields benefits downstream. Data are used from the second year RFT of the District of Columbia privately funded voucher program, supplemented by information obtained from the schools that participating students attended, to identify what school features or practices might be boosting the achievement of voucher students. This preliminary analysis suggests that especially dedicated teachers, a higher proportion of white and higher-income students, and more demanding homework assignments may be the characteristics of private schools that increase the academic achievement of inner-city school voucher users. Additional analyses are recommended before firm conclusions are drawn regarding what happens inside the black box of school voucher experiments. Appended are variables used in the analysis. (Contains 7 tables and 25 references.) (Author/BT)