Effective mental health services require accurate assessment of psychosocial impairments linked to mental health concerns. Youth who experience these impairments do so within and across various contexts (e.g., school, home). Youth may display symptoms of mental health concerns without co-occurring impairments, and vice versa. Yet, nearly all impairment measures presume that those assessed display mental health concerns. Consequently, we recently developed youth and parent versions of a 5-item measure of youth psychosocial impairments (i.e., Work and Social Adjustment Scale for Youth [WSASY]), structured to assess any youth, regardless of mental health status. Across two studies, we developed and tested a WSASY teacher version, in a large sample of 382 student teacher reports (Study 1), and a subsample of 66 youth who, along with their parents and teachers, completed the WSASY and a series of school- and home-based behavioral tasks (Study 2). In Study 1, WSASY teacher reports demonstrated excellent internal consistency and unique relations with teacher reports on well-established measures of psychosocial strengths and difficulties. In Study 2, teacher, youth, and parent WSASY reports demonstrated low correspondence with each other and context-specific relations with criterion variables. This low correspondence allowed us to capitalize on an integrative approach designed to optimize informant-specific variance. Integrative scores demonstrated robust, large-magnitude relations with criterion variables across multiple information sources. These findings provide important psychometric support for use of WSASY teacher reports, and pave the way toward integrating WSASY reports from multiple informants who observe youth psychosocial impairments within different contexts and from different perspectives. [This paper will be published in "Psychological Assessment."