Background: School nurses that are regularly present at school can influence health behaviors in the early lifespan, establishing a foundation for healthy growth. This systematic review identifies activities targeting health promotion and primary prevention and assesses the activities that are effective in improving students' health outcomes. Methods: The protocol was registered on PROSPERO (CRD42023471364). The search was conducted in the databases MEDLINE, PsycINFO, CINAHL, ERIC, Scopus, and ASSIA. Findings: The 19 identified studies include seven RCTs, four quasi-experimental studies, four cross-sectional studies, one secondary data analysis, one qualitative study, and two reviews published between 2012 and 2023. The activities were categorized as health education, screening, and structural prevention. Certain health education activities, commonly in short sessions and incorporating interactive and creative features, effectively improved health behavior, knowledge, and physical health outcomes. One screening intervention reliably identified children with vision abnormalities at an early stage. Implications for School Health Policy, Practice, and Equity: By implementing these activities, school nurses enhance students' health behaviors of nutrition, physical activity, toothbrushing, and nail-biting, among others. In this way, they promote children's well-being and are well positioned to reduce health inequalities. Conclusions: Primary schools are an ideal setting to engage students and their families in enhancing their health literacy, with school nurses incorporating significant potential for public health.