Borderlands of practice are spaces where teachers are engaged in negotiating multiple conceptions of "best practices" within their daily teaching practice. Teachers at work in borderlands must actively negotiate varied conceptions, expectations, and assumptions about what is "best" for their students. These conceptions often challenge teacher professional knowledge and can result in a sense of dissonance about how to best meet the needs of students. Using a case study of one veteran teacher's sense-making processes in her first year of teaching pre-Kindergarten, this article explores how a theoretical lens of dissonance might help researchers and teacher educators to better understand and support teacher identity formation in borderlands of practice.