Median Growth Percentiles (MGPs): Assessment of Intertemporal Stability and Correlations with Observational Scores

While states are no longer required to set up teacher evaluation systems based in significant part on student test scores, quite a few continue to use value-added (VAMs) or student growth percentile (SGP) models for that purpose. In this study, we analyzed three years of teacher data to illustrate the performance of teachers’ median growth percentiles (MGPs)). We found MGP’s consistency over time to be comparable with the existing estimates from the value-added models (VAMs). Additionally, we found that MGPs do not substantively agree with another measure of teacher quality–teachers’ observational scores. These findings suggest that caution should be exercised when teacher’s MGPs, as well as VAMs, are used in teacher evaluation system to make high-stakes decisions such as merit pay, tenure, or teacher contract termination. Our findings about the correlation of MGPs with observational scores support the idea of the multidimensional nature of teacher effectiveness construct.