The art and success of being a competent school administrator relies in large part on the ability to make decisions that address problems effectively, equitably, and efficiently. Despite the importance of this skill, there is a dearth of psychometrically-sound, quantitative measures that focus on school-based administrators (i.e., principals and asst. principals) and the decisions they make. To fill this gap, this study developed and validated a constructed response measure of Administrator Decision-Making in Student Discipline (ADMin-SD). ADMin-SD was developed and validated in three iterative phases: examining the content validity of the items, followed by pilot testing them, and concluding with a field test. The instrument demonstrates adequate reliability and moderate discriminant validity. Implications for researchers include having a tool to conduct future studies of administrator decision-making. As ADMin-SD collects qualitative data and transforms it into quantitative scores, both qualitative and quantitative studies can be conducted. Practitioners have a measurement tool that can help guide instructors of administrative licensure programs in their development of instructional units on decision-making skills. Further, districts and states can identify who is a strong decision-maker in student discipline situations and who needs further professional development.