In this era of high-stakes testing, teachers are often required to follow a standards-based, standardized curriculum, which can be constraining for English to speakers of other languages (ESOL) and mainstream teachers who are trying to meet the needs of English language learners. Despite the challenges presented by such curricula, this study found that one advantage of a standardized, standards-based curriculum is that it can support collaborative efforts between ESOL and mainstream teachers. This research emerged from a university–school district professional development partnership with 26 ESOL and mainstream teachers across 11 elementary schools. This study examined different ways that ESOL and mainstream teachers worked together using a standardized curriculum as a key tool for collaboration. Data collection involved surveys, interviews, and observations of collaborative teaching and coplanning and interviews with three focal teacher pairs before and after they cotaught lessons. The authors found that the ways the teachers used, adapted, and took ownership of the curriculum as a tool for collaboration may have been even more important than the curriculum itself. This study has implications for teachers, schools, and teacher educators considering tools or structures that may already be in place, or that need to be created, which could serve as a common touchstone for collaborative efforts.