Elementary principals regularly engage in classroom observations and teacher evaluations of mathematics instruction. For this work, principals draw upon knowledge of content, pedagogy and leadership skills. Recently, a pedagogical shift toward a more student-centered, constructivist approach to mathematics instruction has occurred. For many current principals, this means a misalignment between the pedagogy they observe and the ways they experienced mathematics as both learner and teacher. Review of the literature suggests the field is limited in knowledge of what principals notice when they engage in classroom observations. This phenomenological study utilizes surveys and interviews of principals to identify what principals attend to when observing and evaluating elementary mathematics instruction. The survey portion involved an 8-minute video of an elementary school mathematics lesson and drew upon the California Standards for the Teaching Profession as a tool for analyzing teacher performance. In interviews, principals were asked to expand upon initial thoughts about the instruction, as well as share thinking about professional learning needs. Key themes arise in the areas of equity, relevant contexts, student thinking/cognitive load, student voice, teacher questioning, problem solving, and goals/objectives. A key finding relates to the notion that while the same aspect of instruction might be attended to, the interpretation of the act can follow a whole range of responses. This study shares important information for designing professional learning opportunities for principals. It highlights the importance of utilizing the collective knowledge of principals in work to advance the efficacy of classroom instruction and calibration of teacher evaluation systems.