Charter schools were developed, in part, to serve as an R&D engine for traditional public schools, Will Dobbie and Roland Fryer note:
In this paper, we collect unparalleled data on the inner-workings of 35 charter schools and correlate these data with credible estimates of each school’s effectiveness.
We find that traditionally collected input measures — class size, per pupil expenditure, the fraction of teachers with no certification, and the fraction of teachers with an advanced degree — are not correlated with school effectiveness.
In stark contrast, we show that an index of five policies suggested by over forty years of qualitative research — frequent teacher feedback, the use of data to guide instruction, high-dosage tutoring, increased instructional time, and high expectations — explains approximately 50 percent of the variation in school effectiveness.
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Indeed, our data suggest that increasing resource-based inputs may actually lower school effectiveness. Schools with more certified teachers have annual math gains that are 0.043 (0.022) standard deviations lower than other schools. Schools with more teachers with a masters degree have annual ELA gains that are 0.034 (0.019) standard deviations lower.
An index of class size, per pupil expenditure, the fraction of teachers with no teaching certification, and the fraction of teachers with an advanced degree, explains about 15 percent of the variance in charter school effectiveness, but in the unexpected direction.