Background/Context: The administration of student discipline is one of many responsibilities under the purview of teachers and educational leaders across the country. Maintaining a safe environment with minimal disruptions is not an easy task. From existing research on student discipline, we have learned that critical examination of data and continuous reflection are important, particularly in light of documented disparities in discipline practices. Under the Individuals with Disabilities Education Act (IDEA), before a school district may discipline a student with a disability for greater than 10 days, it must first conduct what is referred to as a manifestation determination review (MDR) (20 U.S.C. §1415(k)(1)(E)). During this review process, the current version of the law requires school districts to address two questions: (1) Was the student's behavior caused by, or did it have a direct and substantial relationship to, the student's disability? (2) Was the student's misconduct caused by the district's failure to implement the student's individualized education program (IEP), as required by law? This study examines the implementation of this standard. Research Question: This study poses the following research question: What factors (explicit and implicit) influence decision makers when deciding whether a student's misconduct was a manifestation of his or her disability? Research Design: This project used a case study approach to examine 80 MDR decisions in one large urban school district in order to better understand how decision makers implement this standard. Specifically, this study reviewed 40 randomly selected decisions wherein decision makers determined that the student's actions were not a manifestation of his or her disability and 40 randomly selected decisions wherein decision makers determined that the student's actions were a manifestation of his or her disability. Findings/Results: Decision makers cited the academic and behavioral manifestations of students' disabilities, students' behavioral histories, students' ability to control their actions, and connections to the home and community. Despite these consistent factors, the striking similarities between Yes and No decisions illustrates the overall arbitrary nature of the decision-making process. Conclusions/Recommendations: This article discusses implications that attend to both the procedure and substance of manifestation determination review.