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In January 2010, the Massachusetts legislature raised the cap on public charter schools in the state’s lowest-performing school districts. This opened the way for 20 new charter schools state-wide, with 11 slotted for Boston. As the Massachusetts Public Charter School Association (MPCSA) points out, the state legislature recognized the tremendous impact public charter schools have on student performance, and eased the cap with the specific goal of using high-quality charter schools to tackle persistent racial and socioeconomic achievement gaps.
Public charter schools in Boston have demonstrated large increases in achievement (see the 2009 Harvard/MIT study). Specifically, the study found very large gains in both math and reading for middle and high school students attending charter schools in Boston. Further, MPCSA reports that “the five highest performing public high schools are all charters and seven of the eight highest performing public middle schools are charters (based on 2010 MCAS scores comparing open admission public schools).”
Any curious person would ask: Did the policymakers’ decision to lift the cap on the number of charter schools in Massachusetts actually lead to better student outcomes?
As luck would have it, a new working paper by a researcher at MIT takes a very thorough and innovative look at the projected impact of opening new charter schools in Boston and reports: “[S]imulations show that Boston's proposed expansion, which raises the share of middle schoolers attending charters from 9 percent to 15 percent, is expected to reduce the gap in math scores between Boston and the rest of Massachusetts by 10 percent, and reduce citywide achievement gaps by roughly 5 percent.”
Take a look at two of the graphics presented in the paper (see below). Figure 8 shows the projected average test scores of all students in Boston as the number of charter schools increases. The vertical black dotted line indicates the number of charter middle schools as of the 2010-11 school year, and the red dotted line indicates the number of charter middle schools after the proposed number of new schools open. Figure 9 shows the projected achievement gap among all students in Boston as the number of charter schools increases.
Source: Walters, C. (2012). “Predicting the effects of charter school expansion.” MIT working paper, http://economics.mit.edu/files/8138.
The big take away: The presence of more high-quality charter schools leads to higher citywide test scores and smaller achievement gaps throughout the city.
The simulations in the study indicate that there may be a limit in terms of demand to enroll in charter schools at about 24 percent of district market share. However, with 20,000 students on waiting lists to attend the roughly 7,000 seats currently available in charter schools in Boston, and a total of roughly 60,000 students in the district, it is feasible that charter schools could enroll between 40-50 percent of all public school students before demand would taper off. Moreover, if public charter schools produce the type of performance increases (and reductions in the achievement gap) that the simulations project, Boston could see parental demand for access to high-quality charter schools increase as the public sees significant results.
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