Growing interest in understanding the role of students' social-emotional competence for school success necessitates valid measures for large-scale use. We provide validity evidence for the 40-item Washoe County School District Social-Emotional Competency Assessment (WCSD-SECA), a student self-report measure that came from a researcher-practitioner partnership. The WCSD's social and emotional learning standards, which detail when and at what grade students are expected to express different competencies, contributed to hypotheses about the social-emotional competency levels targeted by the WCSD-SECA items. Across two survey years, Rasch analyses showed that the empirical item ordering aligned with the expected ordering to varying degrees, that items better targeted students at low to middle competency levels, and that some items showed differential item functioning across grades and gender/race-ethnicity. Future research can use similar methods to theorize and test how items array along latent competency dimensions in general and for particular subgroups. Especially when accomplished within a researcher-practitioner partnership, such efforts can mutually inform district social and emotional learning standards, helping document student progress in a locally and practically relevant way. By making the WCSD-SECA items freely available, we make it easy for researchers and practitioners to complete future refinements and adaptations.