The theoretical model demonstrates that the intergenerational education mobility of parents’ siblings can enhance parents’ educational efficiency and investment, thereby facilitating children’s intergenerational education mobility. This mobility exerts a significant spillover effect. Empirical analysis using data from the 2018 China Health and Retirement Longitudinal Study reveals that such intergenerational education mobility among parents’ siblings increases the probability of intergenerational education mobility for children whose grandparents and parents have relatively lower levels of education. Specifically, this type of mobility can lead to higher household educational expenditures, improved parental capabilities in information acquisition, and increased emphasis on and expectations for children’s education. These findings provide empirical evidence for the mechanisms underlying educational investment and efficiency. Moreover, the spillover effect of intergenerational education mobility of parents’ siblings is stronger in urban areas than in rural areas. An increase in the number of children’s siblings weakens this spillover effect. Additionally, the spillover effect from mother’s siblings is stronger than that from father’s. These conclusions offer important policy implications for encouraging family virtues such as respecting teachers and valuing education, as well as for strengthening support for family educational resources.