This article reports the robust validation process of the Mathematics Classroom Observation Protocol for Practices (MCOP[superscript 2]). The development of the instrument took into consideration both direct and dialogic instruction encompassing classroom interactions for the development of conceptual understanding, specifically examining teacher facilitation and student engagement. Instrument validation involved feedback from 164 external experts for content validity, interrater and internal reliability analyses, and structure analyses via scree plot analysis and exploratory factor analysis. Taken collectively, these results indicate that the MCOP[superscript 2] measures the degree to which actions of teachers and students in mathematics classrooms align with practices recommended by national organizations and initiatives using a two-factor structure of teacher facilitation and student engagement.