This article from the Journal of Teacher Education considers the measures used to assess the instructional abilities of preservice teachers (PSTs). The authors investigate the reliability and sensitivity of two distinct observation methods used in a teacher preparation program: the Classroom Assessment Scoring System (CLASS) and simulation-based assessments of specific teaching skills. Their findings reveal that both methods have strength; however, they also face significant challenges in accurately and consistently capturing each PST’s individual skills due to external factors such as variable measurement from mentor teachers and other measurement errors. The study highlights the importance of considering the purpose and limitations of different assessment methods to inform teacher preparation.