Although teachers are facing increasing pressure to use data to inform instructional decisions, they often lack the tools to do this. Through the case study of a fourth grade teacher, this paper illustrates how item response theory (IRT) can be used to examine the effectiveness of a teacher's modifications to a classroom assessment and to her teaching practice. The study demonstrates that research methods such as IRT can be used to provide teachers information about the effects of their practice. However, issues of limited resources and sample size must be considered when this method of research is applied to practice at a larger scale.#Prek-12EducationalEvaluation #2012Conference