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 assess ment as an alternative to the conventional approach based on aggregati on of individual scores. The precision provided by the assumed assessm ent design varied dramatically depending on school size and school ave rage ability. For small schools and students with low average abilitie s, 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 comparis ons are clearly identified.