The Behavior Assessment System for Children-Third Edition (BASC-3) is the most recent edition and the Teacher Rating Scales (TRS) was reported to be the most frequently used test in school psychology practice. Despite its popularity, there is a lack of independent empirical research regarding psychometric properties. The BASC-3 Manual, while quite detailed in many respects, lacks important details in reporting TRS item- and scale-level factor analyses limiting confidence in construct validity based on internal structure. The present study examined the latent factor structure of the BASC-3 TRS Preschool, Child, and Adolescent Clinical and Adaptive scales using best practices in exploratory factor analysis (EFA). EFA was conducted with the Clinical and Adaptive scales jointly, and with the Clinical scales separately, to aid interpretive clarity. Results indicated theoretically consistent alignment of the BASC-3 TRS Clinical scales to their specified factors (Externalizing, Internalizing, and School Problems) and an additional factor (Social Disengagement) was identified, suggesting a possible new latent construct for a composite scale score containing the Withdrawal and Atypicality scales. Variance partitioning applied to second-order EFA and model-based validity statistics, however, indicated that the composite scales (Externalizing, Internalizing, School Problems, and Social Disengagement) appear to lack sufficient unique variance for confident clinical interpretation in isolation. (PsycInfo Database Record (c) 2021 APA, all rights reserved).