Background Various milestones have been set targeting the elimination of schistosomiasis with the vision of “a world free of schistosomiasis” including the 2020 and 2025 goals. Despite the increased control and prevention efforts, schistosomiasis still affects many people, partly because treatment doesn’t cover all at-risk populations. Preventive chemotherapy (PC), the cornerstone of control interventions is primarily inclined toward school age children (SAC), whose prevalence also informs interventions for other age groups in the community. Whereas prevalence in SAC has been shown to be a good indicator of the prevalence in other age groups, it remains to be seen as if this is not true in different epidemiological settings and risk areas. Methods This study evaluated the predictive value of schistosomiasis prevalence among SAC in estimating community wide prevalence in Siaya County, Kenya. A single stool sample was collected from participants aged 2-50 years. Stool samples were collected from preschool-age children (2-6 years), SAC (7-14 years), adolescents (15 to 0 to <10%; moderate ≥10% to <50%; and high 35 (≥50%). Results Of the 1,814 participants sampled, 25.6% (95% CI: 23.7-27.7) were infected with S. mansoni. There was no significant difference between the mean egg intensity of S. mansoni in SAC compared to the other age groups. There was a strong positive correlation between SAC prevalence and intensity and community-wide prevalence and intensity; rs =0.8, P<0.001, and rs =0.6, P<0.001, and rs =0.6, P<0.001 respectively. A positive relationship between the overall S. mansoni prevalence and S. mansoni prevalence in SAC was observed. The regression analysis indicated that SAC prevalence/intensity can be used to predict overall S. mansoni prevalence/intensity. In terms of age groups, it can predict in all age groups but adolescents. Conclusions In this setting, generally, the prevalence of S. mansoni among SAC was a good predictor of the prevalence in other age groups and the overall (all age groups combined) prevalence. However, in terms of risk strata SAC data was only a good predictor of overall prevalence and intensity only in the moderate risk stratum. These findings suggest that S. mansoni prevalence and intensity among SAC are valid for community sampling purposes and informing interventions including MDA at the community level.