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The Sensitivity of Value-Added Estimates to Specification Adjustments: Evidence From School- and Teacher-Level Models in Missouri


"We provide a side-by-side comparison of school and teacher growth measures estimated from different value-added models (VAMs). We compare VAMs that differ in terms of which student and school-level (or teacher-level) control variables are included and how these controls are included. Our richest specification includes 3 years of prior test scores for students and the standard demographic controls; our sparsest specification conditions only on a single prior test score. For both schools and teachers, the correlations between VAM estimates across the different models are high by conventional standards (typically at or above 0.90). However, despite the high correlations overall, we show that the choice of which controls to include in VAMs, and how to include them, meaningfully influences school and teacher rankings based on model output. Models that are less aggressive in controlling for student-background and schooling-environment information systematically assign higher rankings to more-advantaged schools, and to individuals who teach at these schools."