There is a growing need for valid measures that can be administered efficiently in school settings to assess the impact of school-based preventive interventions. The current paper aimed to establish a balance among assessment efficiency, reliability, and the measurement properties of an instrument widely used to assess the impact of school-based programs, called the Teacher Observation of Classroom Adaptation-Checklist (TOCA-C; Bradshaw, Debnam, & Leaf, 2010; Koth, Bradshaw, & Leaf, 2009; Werthamer-Larsson, Kellam, & Wheeler, 1991). We leveraged item response theory (IRT) analyses to create a shortened, more focused checklist version of the TOCA-C which is both valid and efficient for large-scale use in schools to track students' behavioral, social-emotional, and family factors over the course of elementary school. The sample included 17,456 children in Kindergarten through grade 5 (47.7% female, 54.2% African American). IRT analyses resulted in the retention of 33 of the original 39 items comprising 7 subscales: (1) "Concentration Problems," (2) "Aggressive/Disruptive Behavior," (3) "Prosocial Behavior," (4) "Emotion Regulation Problems," (5) "Internalizing Problems," (6) "Family Problems," and (7) "Family Involvement." IRT, item difficulty estimates, and confirmatory factor analyses revealed limited evidence of bias based on gender, race, or grade; together, the findings suggested that the 33-item TOCA-C is both a highly valid and reliable measure. [This paper was published in "Children & Schools" v42 n1 p29-40 2020.]