The National Board for Professional Teaching Standards (NBPTS) is the most prominent contemporary effort to professionalize teaching. Along with identifying exceptional teachers, the NBPTS seeks to alter teachers' work by establishing a cadre of expert teachers capable of and obligated to leading school improvement efforts. This article reports findings from a mixed methods study of teachers' responses to the NBPTS in four urban elementary schools. Drawing on institutional theory, the authors find that whether and how the NBPTS enters teachers' work depends on the interplay of professional logics, district and state policy, occupational sentiments, and local school organization.