Student growth percentiles (SGPs) are currently used by several states and school districts to provide information about individual students as well as to evaluate teachers, schools, and school districts. For SGPs to be defensible for these purposes, they should be reliable. In this study, we examine the amount of systematic and random error in…

In achievement testing we assume that students will demonstrate their maximum performance as they encounter test items. Sometimes, however, student performance can decline during a test event, which implies that the test score does not represent maximum performance. This study describes a method for identifying significant performance decline and…

The assessment of differential item functioning (DIF) in polytomous items addresses between-group differences in measurement properties at the item level, but typically does not inform which score levels may be involved in the DIF effect. The framework of differential step functioning (DSF) addresses this issue by examining between-group…