Enrollment Flexibility and Charter School Impacts: The Effect of Backfill on Students in Massachusetts Charter Middle Schools

Authors: Marcus A. Winters, Boston University, Cheonghum Park, Korea Institute of Public Finance

Project Summary

This study leverages Massachusetts’s adoption of a statewide requirement for charter schools to backfill vacancies within some grades to provide the first causal estimates for the effect of incorporating new students on the performance of incumbent charter school pupils. Using data from the universe of Massachusetts public school students enrolled in Grades 5 through 8 from 2007-2008 to 2013-2014, this study compares changes in student achievement in impacted vs. not-impacted grades within Boston charter schools to the patterns of student achievement within traditional public schools and charter schools outside of Boston.

Key Findings

• The backfill requirement meaningfully altered enrollment patterns within charter middle schools in Boston but not within traditional public schools or charter middle schools operating outside of Boston. For example, the requirement increased the proportion of students within a school-grade cohort in an impacted grade within a Boston charter middle school by about 6.7 percentage points relative to non-Boston charter schools.
• Exposure to the backfill requirement under the new law had no significant impact on the test scores of incumbent Boston charter school students

Implications and Recommendations

These findings could be used to support a requirement that charter schools backfill enrollments, but that depends largely on an individual’s view of the importance of charter school autonomy. Nonetheless, the results from Boston should allay concerns that backfilling would harm current student academic performance. These findings also appear to refute claims that comparisons of charter and traditional public school effectiveness are inherently unfair because the option to not backfill contributes substantially to charter schools’ impacts. Why increased backfill had no significant negative impact on the performance of incumbent charter school students is a question worthy of future research.

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