Teacher Quality in Educational Production: Tracking, Decay, and Student Achievement
Growing concerns over the inadequate achievement of U.S. students have
led to proposals to reward good teachers and penalize (or ﬁre) bad ones. The
leading method for assessing teacher quality is “value added” modeling (VAM),
which decomposes students’ test scores into components attributed to student
heterogeneity and to teacher quality. Implicit in the VAM approach are strong
assumptions about the nature of the educational production function and the
assignment of students to classrooms. In this paper, I develop falsiﬁcation tests
for three widely used VAM speciﬁcations, based on the idea that future teachers
cannot inﬂuence students’ past achievement. In data from North Carolina, each
of the VAMs’ exclusion restrictions is dramatically violated. In particular, these
models indicate large “effects” of ﬁfth grade teachers on fourth grade test score
gains. I also ﬁnd that conventional measures of individual teachers’ value added
fade out very quickly and are at best weakly related to long-run effects. I discuss
implications for the use of VAMs as personnel tools.
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