Hoxby study shows impact of Charter schools on attainment


The New York State Charter Schools Act of 1998 authorized the establishment of charter schools in New York State. The first year of operation for charter schools in New York City was 1999-00, and twelve schools were operating by 2000-01.  New York City now has over 100 charter schools although still only  educating  around 5% of the student population.

Joel Klein, the former Head of New York schools, has recently been in the UK telling the story of New Yorks success and Charters role in that success and education reforms more generally.  Almost two years ago, a report The New York City Charter Schools Evaluation Project How New York City’s Charter Schools Affect Achievement on New York City charter schools (2009) written by Hoover Institution scholar Caroline Hoxby with co-authors Sonali Murarka and Jenny Kang reported extremely positively on New Yorks  experience of Charter schools and how they were raising attainment.  The most distinctive feature of the study is that charter schools’ effects on achievement are estimated by the best available, “gold standard” method:  lotteries.  94 percent of charter school students in New York City are admitted to a school after having participated in a random lottery for school places.  This is because the city’s charter schools are required to hold lotteries whenever there are more applicants than places, and the charter schools are routinely oversubscribed.  In a lottery-based study like this one, each charter school’s applicants are randomly divided into the “lotteried-in” (who attend charter schools) and the “lotteried-out” (who remain in the regular public schools).  The authors claim that they are comparing like with like, ie apples with apples. They   follow the progress of ‘ lotteried-in’ and ‘ lotteried-out’ students computing the effect that charter schools have on their students’ achievement .

The reports main finding was that:

‘On average, a student who attended a charter school for all of grades kindergarten through eight would close about 86 percent of the “Scarsdale-Harlem achievement gap” [the difference in scores between students in Harlem and those in the affluent NYC suburb] in math, and 66 percent of the achievement gap in English.’

Hoxbys research has shown good charter results in Chicago too.

The Hoxby report   provides very strong causal evidence that, on average, students in oversubscribed NYC charter schools outperformed their regular public school peers in maths and reading.  The Stanford University study was the most comprehensive look at the city’s charter schools to date. Students who win spots in charter schools outgain those who don’t by 5 points in maths and 3.6 points in reading, on state tests in every year from fourth to eighth grades.

Not everyone, though, accepts Hoxby’s research on Charters at face value. Economist Sean Reardon claims to have found a  couple of serious methodological issues with Hoxby’s research design. And one commentator (see blog link below) believes that the reports executive summary is seriously misleading.


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