Background: Clinical nursing leadership influences patient safety and the quality of care provided. Nurses at all levels require leadership and management skills. Despite recognition of the importance of leadership, student nurses often feel ill prepared to make the transition to Registered Nurse and struggle with prioritisation and delegation. In order to standardise student experience and promote the development of skills and attributes, a leadership and management competency assessment was developed and implemented. Aims: This study aimed to identify the constructs that should be part of an assessment of student nurse competence in relation to clinical nursing leadership, and to evaluate the tool’s reliability. Method: The first phase was to construct the competency assessment tool, using a mixture of deductive methods, including literature and expert review. Second, psychometric evaluation of the tool, including tests to examine its internal consistency and reliability, comparing test and retest reliability, exploratory factor analysis and generalisability theory analysis to identify reliability and sources of error. Results: Five attributes were identified for inclusion in the tool alongside a scale of competence. 150 assessments were conducted with an average time between each assessment of three days. The results show that the tool was consistent over time with no significant difference in the mean scores. The Cronbach alpha was 0.84 and the tool had good internal consistency. The results of the factor analysis revealed loading onto a single construct. Generalisability theory analysis revealed 0.90 global reliability, with students accounting for the majority of the variation in scores. Conclusions: The Leading and Managing Care assessment tool represents a valid and reliable assessment of student nurse competence to lead care delivery. Use of the tool during practice placement allows for a structured approach to the development of skills around prioritisation, management of resources, communication and the management of risk.