Creating equitable opportunities so all students can learn and succeed mathematically has been a key focus of mathematics education across several decades. Central to student achievement are students' mathematical identity and their feelings of success during instruction. Researchers (e.g., Boaler & Staples, 2008) have shown that teachers can be particularly powerful in shaping students' beliefs, feelings of success, and achievement, but few studies have investigated how teachers frame what it means to be successful or "smart" in mathematics. Through the social construct of smartness (Hatt, 2012) and the learning perspectives of incremental and entity theories (Blackwell, Trzesnieski, & Dweck, 2007; Yeager & Dweck, 2012), I examine how one teacher, Mrs. Purl, conceptualized what it meant to be smart in mathematics and how this perception changed slowly, over time, through repeated examination and discussion of individual student's thinking. As Mrs. Purl came to know her students at a personal level, she began to see that her perceptions were not always accurate and warranted reexamination.