There is an increasing interest of policies and projects to adapt boarding schools as a means to provide quality education for educationally disadvantaged students. However, little evidence is available for the effectiveness of boarding schools. The current study examined the boarding effect on primary and middle school student mathematics achievement using stratified analysis and propensity score matching approach. The boarding on campus showed a negative and insignificant effect on fourth-grade student mathematics achievement, but a significantly positive effect on eighth-grade student achievement. The mechanisms through which boarding on campus might affect boarders' achievement were also explored.