School voucher programs are scholarship initiatives -- frequently government funded or incentivized -- that pay for students to attend private schools of their choice. This study is the first formal meta-analytic consolidation of the evidence from all randomized controlled trials (RCTs) evaluating the student-level math and reading test score effects of school vouchers internationally. Our search process turned up 9,443 potential studies, 21 of which were ultimately included. These 21 studies represent 11 different voucher programs. Utilizing a random effects and robust variance estimation framework, we find moderate evidence of positive achievement impacts of private school vouchers, with substantial effect heterogeneity across programs and outcome years. Suggestive evidence exists that voucher interventions may be cost effective even for null achievement impacts. Future experimental studies of long-term, scaled up voucher interventions could strengthen our understanding of achievement impacts.