Psychosocial functioning plays a key role in students' wellbeing and performance inside and outside of school. As such, techniques designed to measure and improve psychosocial functioning factor prominently in school-based service delivery and research. Given that the different contexts (e.g., school, home, community) in which students exist vary in the degree to which they influence psychosocial functioning, educators and researchers often rely on multiple informants to characterize intervention targets, monitor intervention progress, and inform the selection of evidence-based services. These informants include teachers, students, and parents. Across research teams, domains, and measurement methodologies, researchers commonly observe discrepancies among informants' reports. We review theory and research--occurring largely outside of school-based service delivery and research--that demonstrates how patterns of informant discrepancies represent meaningful differences that can inform our understanding of psychosocial functioning. In turn, we advance a research agenda to improve use and interpretation of informant discrepancies in school-based services and research. [This paper was published in "Journal of School Psychology" v74 p74-89 Jun 2019.]