This article reports findings from a qualitative study exploring mentors' reluctance to refer students who did not perform adequately in clinical settings. A focus group and individual semi-structured interviews were undertaken with experienced stage two mentors in an NHS trust. Mentors spoke of having to balance objectivity and intuition when dealing with upset or angry students, those who were popular or those who tried hard but did not perform adequately. They describe a number of factors that led them to pass a student who was less than satisfactory. In particular the findings highlight difficulties with measuring and recording attitudes. The data demonstrate the willingness and motivation of mentors to keep up to date and learn from their students. However, findings also suggest the need for mentors to have greater confidence in their own clinical abilities. Recommendations are made for training strategies to address these barriers in order to ensure that only competent, caring nurses are allowed to register.