School-Level IRT Scaling of Writing Assessment Data

School-level assessment of student writing ability using a group-level, polytomous item response theory (IRT) model was illustrated in this study. The study supported the viability of an IRT-based school assessment as an alternative to the conventional approach based on aggregation of individual scores. The precision provided by the assumed assessment design varied dramatically depending on school size and school average ability. For small schools and students with low average abilities, differences in average school performance had to be quite large to be trustworthy. In contrast, the design provided greater precision in detecting differences for large schools and students with high average abilities. An operational use of this design would require great care in the reporting of results to ensure that unreliable school comparisons are clearly identified.