Positive relationships with teachers are important for students’ second language motivation. However, little is known about how interpersonal interactions stimulate motivated behavior. Drawing on studies of teacher-student relationships, theories from positive psychology, and the psychology of unconscious self-regulation, this case study examines moments of teacher-student interaction and explores influences on students’ engagement and motivation. Observations (N = 15) were carried out in 2 classrooms, and interviews with the focal teacher of this study and her students were conducted. Data were analyzed using a grounded theory ethnography approach. Findings indicate that moments of close personal contact and their influences may differ in emerging and mature teacher-student relationships. While in emerging relationships moments of contact can have immediate influences on engagement and motivation, in mature relationships influences on learning behavior may be less pronounced and involve unconscious motivational processes. The study’s methodological limitations are discussed and proposals are made for future ethnographic and experimental work.