Charter schools are publicly funded but operate outside the regulatory framework and collective bargaining agreements characteristic of traditional public schools. In return for this freedom, charter schools are subject to heightened accountability. This paper estimates the impact of charter school attendance on student achievement using data from Boston, where charter schools enroll a growing share of students. We also evaluate an alternative to the charter model, Boston's pilot schools. These schools have some of the independence of charter schools, but operate within the school district, face little risk of closure, and are covered by many of same collective bargaining provisions as traditional public schools. Estimates using student assignment lotteries show large and significant test score gains for charter lottery winners in middle and high school. In contrast, lottery-based estimates for pilot schools are small and mostly insignificant. The large positive lottery-based estimates for charter schools are similar to estimates constructed using statistical controls in the same sample, but larger than those using statistical controls in a wider sample of schools. The latter are still substantial, however. The estimates for pilot schools are smaller and more variable than those for charters, with some significant negative effects.
The authors are grateful to the Boston Foundation for financial support and to Boston's charter schools, the Boston Public Schools, and Carrie Conaway, Mary Street, and the staff of the Massachusetts Department of Elementary and Secondary Education for data and assistance. Sarah Cohodes, Jon Fullerton and the staff of the Center for Education Policy Research at Harvard University played a critical role in this project. We also thank Bruno Ferman, Yuqiao Huang, Simone Schaner, Chris Walters, and Victor Vazquez for expert research assistance. We benefited from comments by Derek Neal and seminar participants at the Bank of Italy, the LSE, McGill, the New York Fed, UBC, UC Dublin, UCLA, UC Riverside, UIUC, ZEW, and the November 2009 New Directions in the Economic Analysis of Education Conference at the University of Chicago. Abdulkadiroglu acknowledges an NSF-CAREER award. Pathak thanks the Rappaport Institute for Greater Boston for research support. The views expressed herein are those of the author(s) and do not necessarily reflect the views of the National Bureau of Economic Research.