This article presents the psychometric properties of the evidence-based practice (EBP) instrument (School Version), a new interdisciplinary measure for understanding and measuring EBP use that can be understood and used across the three professions who provide the most mental health services in schools. The instrument was developed based on theory, review of the literature, expert review (N = 12), pilot study (N = 20), and national study (N = 303). While the measure may have applicability for other groups of mental health providers in other settings, this study focused on the perspectives of mental health providers in schools, specifically school psychologists, school counselors, and social workers. Initial psychometric examination resulted in a 13-item, one factor model and indicated preliminary evidence for strong validity and internal reliability. No significant difference in total score among groups of mental health professionals was found, suggesting similarities of comprehension and application of EBP regardless of professional discipline. This instrument is the only one of its kind and provides a helpful first step towards common language and common goals when conceptualizing what it means for mental health providers to use best practice. Implications for school professionals and future research are offered.