Should Value-Added Models Control for Student Absences?
by Seth Gershenson - September 01, 2016
Background: Whether or not value-added models should control for contemporaneous student absences is theoretically ambiguous, as such absences are only partly outside of teachers’ control. Teachers often feel strongly that value-added models should account for student attendance, and many districts’ value-added models condition on lagged student absences as a result.
Objective: Using matched teacher-student administrative data from a statewide longitudinal data system, this note investigates the practical importance of this modeling decision for value-added measures of teacher effectiveness (VAMs).
Research Design: This is a secondary analysis.
Analysis: I compare VAM-based rankings of teacher effectiveness generated by value-added models that either control for current absences, control for lagged absences, or exclude student absences altogether.
Findings: Regardless of how between-school differences are accounted for, VAM-based rankings of teacher effectiveness are insensitive to how, and whether, student absences enter the value-added model’s conditioning set. Spearman Rank Correlations are always larger than 0.99 for both math and reading VAMs, suggesting that whether or not value-added models control for student absences is a relatively unimportant modeling decision, at least in the context of self-contained primary school classroom teachers.
Conclusions: These results are consistent with recent research suggesting that simply conditioning on lagged achievement yields approximately unbiased VAMs. Moreover, assuming no behavioral response on the part of teachers, these findings suggest that controlling for student absences in teacher evaluation systems’ value-added models is a relatively inexpensive way to increase teacher buy-in.
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