The Classroom Strategies Assessment System-Observer Form (CSAS-O) is a classroom observational system that combines direct observations and rating scales to assess teacher instructional and behavioral management practices, inform goals, plan professional development interventions, and monitor progress. CSAS-O Strategy Rating Scales yield scores indicating the discrepancy between the frequency with which observed teachers use evidence-based strategies and the recommended frequency with which they should use strategies during specific lessons. An illustrative example is provided along with a summary of reliability and validity evidence. Dudek, Reddy, Lekwa, & Hua write about Improving Universal Classroom Practices through Teacher Formative Assessment and Coaching using the CSAS-O in the current issue.