Recent research on the relationship between standards and teachers' practice suggests that teachers are unlikely to make changes to practice without extensive opportunities for learning about standards with colleagues. This article extends this line of research, using a comparative case study of three high-poverty urban schools to examine the nature of teachers' collaborative work around the Common Core State Standards and the conditions that support this work. It argues that collaborative practices that encourage joint examination of instruction and student learning against standards support teachers in noticing and attending to differences between their current practice and standards. In addition, it examines the role of teachers' instructional knowledge and principals' leadership in supporting teachers' collaboration around standards.