Handwashing is crucial for preventing infectious diseases among primary school students in Northern Nigeria where hygiene practices are often inadequate. A comprehensive search strategy was employed to identify relevant studies, which were critically appraised using predefined inclusion and exclusion criteria. Data synthesis included thematic analysis and meta-analytic techniques where applicable. Handwashing frequency increased by 20% among students exposed to intervention programmes compared to controls, with a median improvement of three hand washes per day in the intervention group. School-based interventions significantly enhanced handwashing habits among primary school students in northern Nigeria over one year. Further research should explore long-term effects and cost-benefit analyses of these interventions to inform policy development. Handwashing, Primary School Students, Northern Nigeria, Interventions, One-Year Outcomes Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.