Although interest in social-emotional learning (SEL) is growing, there are few efficient measures of SEL constructs, especially those of the popular CASEL Framework. To address this need, the SSIS SEL Brief Scales (SSIS SEL"b") were developed. Initial evidence for the SSIS SEL"b" is promising, but evidence is needed for its structural validity. The purpose of this study was to provide such evidence. We used confirmatory factor analysis to evaluate six plausible structures of the SSIS SEL"b"-Teacher (n = 643) and SSIS SEL"b"-Student (n = 530) forms with a large sample collected from two Midwestern private/parochial schools. Results indicated each of the models were defensible, but all models pointed to the conclusion that applied use should focus on the overall SEL Composite score. Findings provided support for the SSIS SELb Scales and indicated the need for future research better explicating the theoretical specifics of the CASEL Framework.