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Charter Schools: Are They Effective?

Designed to free educators from bureaucratic regulations and encourage innovations, charter schools are public schools that have been granted autonomy over their operations. They operate under a contract, or charter, with their state that specifies the conditions under which a school can operate and holds the school accountable for meeting certain terms, such as improving student performance. Since their inception in 1992, charter schools have played an important part in education reform. By January 2005, they had been authorized in 40 states, the District of Columbia, and Puerto Rico, and nearly 4,000 charter schools were serving more than one million students in these locations.

At the same time, some have questioned whether charter schools promote student learning adequately, while others have raised concerns that charter schools admit only the most motivated students and may exacerbate racial segregation in public schools. Some critics have called for greater oversight of charter schools.

Mathematica conducted a national evaluation of charter schools, funded by the U.S. Department of Education, to address three key research questions:

  • What are the impacts of charter schools on students' achievement, students' school success, and parents' satisfaction?
  • In what ways are charter schools and conventional public schools different? What role do these differences play in determining student outcomes?
  • To what extent does the autonomy or policy environment under which charter schools operate influence their effectiveness?

The evaluation was based on an experimental design whereby applicants are assigned by lottery to groups that are either admitted or not admitted to the school. The evaluation included the following components:

  • Selection and recruitment of 36 charter middle schools. To be eligible for the study, the schools had to have been operating for at least two years and had to be oversubscribed—that is, to have more applicants than spots available at the school. Schools were selected for the study from 15 states covering a broad geographic area and with laws that vary in the degree of autonomy offered to charter schools.
  • Random assignment of charter school applications through lotteries for admission at participating schools. Participating charter schools conduct lotteries as part of their admissions process, and these lotteries separate applicants into two groups: (1) applicants who were offered admission to the school by lottery, and (2) lottery participants who were not offered admission. We estimated the impacts of charter schools by tracking these two groups and comparing their outcomes over a two-year follow-up period.
  • Data collection on sample members over a baseline year and a two-year follow-up period. Quantitative data collection includes administrative school records data on students' attendance, performance on standardized tests, and other outcomes; telephone surveys of students and their parents; and a mail survey of school principals.


  • We found that, on average, charter schools had no significant impacts on student achievement in math and reading.
  • Impacts on measures of both student and parent satisfaction were statistically significant.
  • We found that charter school impacts varied widely across schools.
  • Impacts were most positive among schools in large, urban areas and among those serving the most disadvantaged students.


"Do Charter Schools Improve Student Achievement? Evidence from a National Randomized Study" (December 2011)
"Using Lotteries to Evaluate Schools of Choice: Evidence from a National Study of Charter Schools" Economics of Education Review (July 2011)
"The Evaluation of Charter School Impacts" (June 2010) Executive Summary
"Charter School Study Q&A" (June 2010)