In this study, Will Dobbie and Roland G. Fryer, Jr. collect data on the inner-workings of 39 charter schools and correlate these data with school effectiveness. They find that traditionally collected input measures – class size, per-pupil expenditure, teacher certification, and teacher training – are not corelated with school effectiveness. In stark contrast, they show that an index of five policies suggested by qualitative research – frequent teacher feedback, the use of data to guide instruction, high-dosage tutoring, increased instructional time, and high expectations – explains approximately half of the variation in school effectiveness.