Developmental psychopathology researchers and practitioners commonly conduct behavioral assessments using multiple informants' reports (e.g., parents, teachers, practitioners, children, and laboratory observers). These assessments often yield inconsistent conclusions about important questions in developmental psychopathology research, depending on the informant (e.g., psychiatric diagnoses and risk factors of disorder). Researchers have theorized why informant discrepancies exist and advanced methodological models of informant discrepancies. However, over 50 years of empirical data has uncovered little knowledge about these discrepancies beyond that they exist, complicate interpretations of research findings and assessment outcomes in practice, and correlate with some characteristics of the informants providing reports (e.g., demographics and mood levels). Further, recent studies often yield take-home messages about the importance of taking a multi-informant approach to clinical and developmental assessments. Researchers draw these conclusions from their work, despite multi-informant approaches to assessment long being a part of best practices in clinical and developmental assessments. Consequently, developmental psychopathology researchers and practitioners are in dire need of a focused set of research priorities with the key goal of rapidly advancing knowledge about informant discrepancies. In this paper, I discuss these research priorities, review work indicating the feasibility of conducting research addressing these priorities, and specify what researchers and practitioners would gain from studies advancing knowledge about informant discrepancies in developmental psychopathology research.