The emotional well-being of individuals is largely dependent on the quality of their social relationships, as acknowledged by self-determination theory and the belongingness hypothesis. While the significance of high-quality relationships for teachers has received increasing attention in empirical research, little is known about the impact of social relationships on student teachers' emotions in the practicum, especially from a quantitative perspective and considering multiple relationship qualities simultaneously. Research on this topic is highly topical as emotions have been found to be important drivers both for professional behaviour in the classroom and professionalisation processes in general. Against this backdrop, our study examined how the quality of social relationships between students in class, mentor teachers, and fellow student teachers influences the development of emotional experiences of student teachers in a school practicum. We conducted an online survey with 203 Austrian student teachers studying secondary education, inquiring about their emotional experiences and social relationships before and after their practicum. The results revealed that the quality of relationships with students in class was the most influential factor determining changes in student teachers' emotional states during their practicum. These findings emphasise the importance of cultivating positive relationships with students in the classroom, especially during the school practicum in teacher education.