This paper analyses, in terms of social facilitation and stress theories, some of the effects of the presence and actions of instructors on student nurses’ behaviour. The theories imply the existence of a paradox in the training of nurses. The aim of teaching is to reduce errors. Much of the training is done in the presence of instructors and patients. However, the presence of significant others during learning is hypothesized to increase errors, due to fear of failure and embarrassment. Indeed, the analysis of students’ self-reports describing stressful encounters with instructors indicates that the students tended to perceive the instructors as mainly evaluative. One possible solution to this paradox is to distinguish clearly between the instructive and evaluative roles, to de-emphasize evaluation, especially during learning, thus (a) reducing potential sources of anxiety and (b) creating a more supportive learning atmosphere. It is also suggested that both instructors and students may benefit from stress-reduction strategies, such as relaxation training and improved communication.