This paper discusses a study examining how mentors in nurse education make professional judgments about the clinical competence of their pre-registration nursing students. Interviews were undertaken with nine UK students and 15 mentors, using critical incidents in practice settings as a focus. The study was undertaken for the English National Practice-Based Professional Learning Centre for Excellence in Teaching and Learning. This paper reports on the conversation analytic thread of the work. The mentor role with pre-registration nursing students is not only supportive but involves formal assessment. Central to the relationship is communication. In professional education, communication is seen as a skill to be applied and assessed in practice settings but is also the medium mentors and mentees use to talk about the relationship. Analysis of excerpts of conversation in the interviews shows that episodes of communication are used as topics of conversation to establish professional identity. It also reveals that judgments about the extent of professional capacity of both students and mentors are grounded in everyday behaviours (for example, enthusiasm, indifference and confidence) as well as professional competence. In addition to focusing on clinical issues, mentors can and do use mundane communication as a resource for judgments about competence.