work is licensed under a Creative Commons IGO 3.0 AttributionNonCommercial-NoDerivatives (CC-IGO BY-NC-ND 3.0 IGO) license (http://creativecommons.org/licenses/by-nc-nd/3.0/igo/ legalcode) and may be reproduced with attribution to the IDB and for any non-commercial purpose, as provided below. No derivative work is allowed.Any dispute related to the use of the works of the IDB that cannot be settled amicably shall be submitted to arbitration pursuant to the UNCITRAL rules. The use of the IDB's name for any purpose other than for attribution, and the use of IDB's logo shall be subject to a separate written license agreement between the IDB and the user and is not authorized as part of this CC-IGO license.Following a peer review process, and with previous written consent by the Inter-American Development Bank (IDB), a revised version of this work may also be reproduced in any academic journal, including those indexed by the American Economic Association's EconLit, provided that the IDB is credited and that the author(s) receive no income from the publication. Therefore, the restriction to receive income from such publication shall only extend to the publication's author(s). With regard to such restriction, in case of any inconsistency between the Creative Commons IGO 3.0 Attribution-NonCommercial-NoDerivatives license and these statements, the latter shall prevail.Note that link provided above includes additional terms and conditions of the license. In an effort to boost student achievement and reduce income-based gaps, the Chilean government passed the Preferential School Subsidy Law (SEP) in 2008, which altered the nation's 27-year-old universal school-voucher system dramatically. Implementation of SEP increased the value of the school voucher by 50 percent for "priority students", primarily those whose family incomes fell within the bottom 40 percent of the national distribution. To be eligible to accept the higher-valued vouchers from these students, schools were required to waive fees for Priority students and to participate in an accountability system. We addressed these RQs by fitting a sequence of multi-level interrupted time-series regression models, supplemented by other descriptive analyses. We found that:1. On average, student test scores increased markedly and income-based gaps in those scores declined by one-third in the five years after the passage of SEP.2. The combination of increased support of schools and accountability was the critical mechanism through which the implementation of SEP increased student scores, especially in schools serving high concentrations of low-income students. Migration of lowincome students from public schools to private voucher schools played a small role.We conclude by responding to a recent paper by Feigenberg, Rivkin, and Yan (2017) that argues that the gains from SEP are illusory. *The authors would like to acknowledge the helpful comments on earlier drafts provided