AIM: This study aims to achieve two objectives. The first is to evaluate the feasibility, validity and reliability of Script Concordance Test (SCT) designed to assess the clinical reasoning (CR) skills of nurses working in a Pediatric Surgery Intensive Care Unit (PSICU). The second is to investigate the impact of different reference panels on SCT scores. BACKGROUND: Although the SCT is widely used to assess CR in nursing students, its application in postgraduate nursing practice remains underexplored. DESIGN: A descriptive evaluation and a validation study. METHODS: A 13-case SCT, was administered to 30 nurses working in the PSICU. The scoring key for the SCT was developed based on three distinct panels. The scores of experts and participants were compared using a t-test. Reliability was assessed through generalizability (G) theory. A decision (D) study conducted within the G theory framework determined the number of cases and items required to achieve optimal reliability. RESULTS: A statistically significant difference in SCT scores was observed across the three-panel compositions. SCT demonstrated its ability to effectively distinguish between experts and participants. The highest reliability (0.71) was achieved with the mixed panel scoring. According to the D study, achieving a reliability of 0.80 or higher requires 100 items. CONCLUSION: The SCT can be recommended as a tool that provides valid and reliable measures for assessing CR in postgraduate nursing practice. When developing the scoring key for the (SCT), it is advisable to use either a panel consisting solely of nurses or a mixed reference panel.