In this paper, we critically examine the way in which scholars have traditionally defined and problematized attrition. Through a series of examples of large-scale intervention impact studies, we share insights about the sources and consequences of attrition that expand our notion of how and why attrition occurs. We also discuss potential steps for anticipating, mitigating, and responding to attrition in the dynamic context of schooling. By expanding our understanding of attrition, we hope to engage the field in further dialogue that could lead to policies and practices that might lessen the potential impacts not only on our ability to conduct research, but also our ability to advance the learning of teachers and their students.