Teacher shortages have led to vacancies in schools that are often filled with student teachers who are not yet fully qualified but want to gain practical experience. When student teachers begin working in the classroom, they face professional challenges that can lead to high levels of work-related stress. Based on assumptions drawn from the job demands-resources (JD-R) model, we surveyed n = 172 student teachers from Germany and found that more complex instructional activities (e.g., teaching classes on their own) are associated with higher work-related stress. While social support from colleagues moderates this relationship, student teachers’ self-efficacy beliefs do not.