Background/Objectives: The assessment of clinical competencies in nursing education requires valid and reliable instruments, especially for essential procedures such as the placement of a cervical collar in the care of polytrauma patients. The objective of this study was to analyze the psychometric properties of a rubric designed to assess the placement of cervical collars in nursing students in a low-fidelity clinical simulation environment. Methods: A quasi-experimental, cross-sectional study was conducted with 186 undergraduate nursing students, organized into 62 groups, over three academic years (2021–2024). An 8-item rubric was applied, with a 4-level Likert scale (1–4). Interrater reliability was analyzed using Cohen’s Kappa index, internal consistency using Cronbach’s alpha, and the internal structure of the instrument using exploratory factor analysis, applying Varimax orthogonal rotation. Results: Inter-rater reliability showed values ranging from moderate to substantial, with greater agreement observed in items related to the selection of the collar and the position of the medical team, and moderate agreement in those related to technical maneuvers and immobilization. The rubric showed adequate overall internal consistency (α = 0.76), with good to very good consistency values in 6 of the 8 items. Exploratory factor analysis identified a two-dimensional structure with a dominant procedural factor (4 items) and a second factor associated with clinical judgment (4 items). Conclusions: The validated rubric has adequate levels of reliability and internal consistency for evaluating the placement of cervical collars by nursing students. Its application can promote more objective and structured evaluation processes in clinical simulation for nursing students, contributing to the development of essential skills in the care of polytrauma patients.