The inadequacies of charter schools have been confirmed by many recent studies. Even CREDO , which is part of a conservative think tank funded by the pro-privatization Walton Foundation, recently found that in comparison to traditional public schools “students in Ohio charter schools perform worse in both reading and mathematics.” Another recent CREDO study  of California schools reached mixed results, with charters showing higher scores in reading but lower scores in math.
In a study of Chicago’s public schools, the University of Minnesota  Law School determined that “Sadly the charter schools, which on average score lower that the Chicago public schools, have not improved the Chicago school system, but perhaps made it even weaker.”
In general, as concluded  by the nonpartisan Spencer Foundation and Public Agenda, “There is very little evidence that charter and traditional public schools differ meaningfully in their average impact on students’ standardized test performance.” Another report from Data First , part of the Center for Public Education, stated that “the majority of charter schools do no better or worse than traditional public schools.”
But there’s a lot of data that leans toward “worse” rather than “better.” A Brookings report  showed underperformance in Arizona’s charter schools. An In the Public Interest  group found that an analyst for the District of Columbia “could not provide a single instance in which its strategy of transferring a low-performing school to a charter management organization had resulted in academic gains for the students.” The Minnesota Star Tribune  reported that “Students in most Minnesota charter schools are failing to hit learning targets and are not achieving adequate academic growth.” Over 85 percent  of Ohio’s charter students were in schools graded D or F in 2012–2013. In the much-heralded New Orleans charter experiment, the Investigative Fund  found that “eight years after Hurricane Katrina…seventy-nine percent of RSD charters are still rated D or F by the Louisiana Department of Education.”
Charters Won’t Tell Us What They’re Doing