Researchers and practitioners sometimes presume that using a previously "validated" instrument will produce "valid" scores; however, contemporary views of validity suggest that there are many reasons this assumption can be faulty. In order to demonstrate just some of the problems with this view, and to support comparisons of…

Mean or median student growth percentiles (MGPs) are a popular measure of educator performance, but they lack rigorous evaluation. This study investigates the error in MGP due to test score measurement error (ME). Using analytic derivations, we find that errors in the commonly used MGP are correlated with average prior latent achievement: Teachers…