Another neat paper on teacher value-added contributes to the growing consensus around the factors that help identify effective teachers. From How and Why do Teacher Credentials Matter for Student Achievement?, by Clotfelter, Ladd and Vigdor:
Our findings for the experience variables are fully consistent with those of other studies, including our own previous cross sectional analysis. In particular, close to half the achievement returns to experience arise during the first few years of teaching but returns continue to rise throughout most of the experience range. Furthermore it appears that all of the returns are attributable to experience per se rather than to differential rates of attrition between more or less effective teachers. In addition to the findings for experience, we also document that the stateâ€™s licensure tests provide policy relevant information, especially with respect to the teaching of math; that the form of licensure matters; that the National Board Certification process appears to identify effective teachers but does not make them more effective; and that masterâ€™s degrees obtained after 5 years of teaching are associated with negative effects on student achievement.Â … The real challenge for policy makers is to find ways to direct the teachers with strong credentials to the students who most need them.