A series of studies extended psychometric research on the Adjustment Scales for Preschool Intervention (ASPI). The ASPI is a multidimensional measure of preschool emotional and behavioral adjustment for use within formal early childhood educational programs. These studies used a multiple method, multisource approach to provide additional evidence for the reliability and validity of the ASPI. Findings documented inter-rater reliability of the ASPI across key informants within early childhood educational programs—teachers and teacher assistants. Findings supported concurrent validity of the ASPI with direct observations of preschool classroom adjustment problems and the developmentally salient constructs of temperament and emotion regulation. Implications for policy, practice, and future research are discussed. © 2004 Wiley Periodicals, Inc. Psychol Schs 41: 725–736, 2004.