It has long been argued that U.S. states' differential performance on nationwide assessments may reflect differences in students' opportunity to learn the tested content that is primarily due to variation in curricular content standards, rather than in instructional quality or educational investment. To quantify the effect of differences in…

This study examined the validity of test accommodation in third-eighth graders using differential item functioning (DIF) and mixture IRT models. Two data sets were used for these analyses. With the first data set (N = 51,591) we examined whether item type (i.e., story, explanation, straightforward) or item features were associated with item…