Schools are important arenas for mental health promotion initiatives. School nurses have the opportunity and ability to support and promote students’ mental health, but their role and practices have been perceived as somewhat unclear. Therefore, the aim of this study was to explore school nurses’ mental health promotion practices. A total of 12 scientific studies were synthesized through a meta-ethnographic approach. The overarching results of the synthesis show that school nurses’ mental health promotion practices are largely about balancing and combining the students’ needs with different professional perspectives, competencies, and conditions. The school nurses perceived that they had the power to influence their practices through a variety of ways, highlighting the importance of letting the students’ needs guide the practices. Yet, at the same time they described feelings of powerlessness because of the different organizational structures that were hindering their mental health promotion practices.