Video is used extensively in teacher preparation, raising questions about what and how preservice teachers learn through video observation and analysis. We investigate the development of candidates' noticing of ambitious mathematics pedagogy in the context of a video-based course designed to cultivate ways of seeing and interpreting classroom interactions. Qualitative analysis of candidates' observations of teaching at the beginning and end of the course generated a framework of practices and associated approaches for noticing instructional interactions. The 3 practices include "attending to features of instruction," "elaborating on observations," and "integrating observations to reason about instruction." Findings reveal that variations in candidates' noticing was tied to their attention to the details of the features of ambitious pedagogy and to the extent to which they integrated observations to examine the relation between student thinking, teaching practice, and mathematical content.