Poor nutrition and inadequate WASH (water, sanitation, and hygiene) practices significantly impact children’s health, nutrition, and cognitive development, especially in low-income settings. These factors further aggravate the incidence of undernutrition, weaken the immune system, increase susceptibility to illnesses and reduce cognitive performance. Evidence on the effectiveness of existing WASH interventions is needed. This review evaluated the effectiveness of nutritional and WASH interventions on the academic performance of children in Ethiopia. A systematic search of Cochrane, DOAJ, Google Scholar, and PubMed (2010–2024) was conducted using MeSH terms and keywords related to WASH. Two independent reviewers screened studies and extracted data. Eligible studies included cross-sectional and cohort studies on Ethiopian schoolchildren with quantifiable academic outcomes. The JBI SUMARI was used to assess bias, and the GRADE approach was used to evaluate evidence quality. The meta-analysis used a random-effects model in Stata and reported pooled RRs with 95% CIs. Subgroup and sensitivity analyses examined moderators such as study design, intervention type, and sample size. A total of 19 studies, 16 cross-sectional (n = 16) and three prospective (n = 3) cohort studies with a total of 9034 participants, were included. The random effects model revealed a significant improvement in academic performance among students receiving both nutrition and WASH, with a pooled large positive effect size of 2.05 (95% CI: 1.26, 2.28; I2=). In the subgroup meta-analysis, the effect of the intervention was more positive among those who skipped breakfast (3.47, 95% CI: 0.47, 6.47), chronic iodine deficiency (4.49, 95% CI: 4.08, 4.90), food insecurity (2.810, 95% CI: 1.281, 4.339), and underweight (0.61, 95% CI: 0.46, 0.75). Despite moderate variability and some risk of bias, the evidence supports the integration of comprehensive nutrition and WASH programs into school health initiatives. Future research should focus on long-term effects and cost-effectiveness.