Prior test scores do not provide valid placebo tests of teacher switching research designs
Chetty, Friedman, and Rockoff (2014)[CFR] evaluate the degree of bias in teacher value-added (VA) estimates using a “teacher switching” research design, regressing changes in mean test scores across cohorts on changes in mean teacher VA. Recent studies (Kane, Staiger, and Bacher-Hicks 2014, Rothstein 2014) have found that regressing changes in mean scores in the prior grade on changes in mean VA also yields a positive coefficient, a result we confirm in our data.