Value-added models and the measurement of teacher productivity

• We test many of the central assumptions required to derive value-added models.
• Empirically, we reject nearly all assumptions underlying value-added models.
• We find that teacher value-added estimates are highly sensitive to model specification.

Research on teacher productivity, as well as recently developed accountability systems for teachers, relies on “value-added” models to estimate the impact of teachers on student performance. We consider six value-added models that encompass most commonly estimated specifications. We test many of the central assumptions required to derive each of the value-added models from an underlying structural cumulative achievement model and reject nearly all of them. While some of the six popular models produce similar estimates, other specifications yield estimates of teacher productivity and other key parameters that are considerably different.