Purpose To develop an evaluation system of clinical competencies for the practicum of nursing students based on the Nursing Interventions Classification (NIC). Design and Methods Psychometric validation study: the first two phases addressed definition and content validation, and the third phase consisted of a cross-sectional study for analyzing reliability. The study population was undergraduate nursing students and clinical tutors. Findings Through the Delphi technique, 26 competencies and 91 interventions were isolated. Cronbach's α was 0.96. Factor analysis yielded 18 factors that explained 68.82% of the variance. Overall inter-item correlation was 0.26, and total-item correlation ranged between 0.66 and 0.19. Conclusions A competency system for the nursing practicum, structured on the NIC, is a reliable method for assessing and evaluating clinical competencies. Further evaluations in other contexts are needed. Clinical Relevance The availability of standardized language systems in the nursing discipline supposes an ideal framework to develop the nursing curricula. [ABSTRACT FROM AUTHOR]