From siblings to skills: How does sibling structure shape children's academic achievement and non-cognitive...

This study investigates how sibling structure, encompassing sibling size, gender composition, and birth order, shapes academic achievement and non-cognitive development among children in rural Northwest China. Leveraging two-period panel data from 5397 elementary school students across 135 rural schools, we employ ordinary least squares (OLS) regression, propensity score matching (PSM), and instrumental variable (IV) approaches to address endogeneity and identify causal mechanisms. Results show that larger sibling sizes and later birth orders have significant negative effects on academic achievement and key non-cognitive traits such as extraversion, agreeableness, and openness. Gender disparities emerge as having brothers exacerbates deficits in non-cognitive traits, while sisters show negligible effects. Heterogeneity analysis suggests that larger sibling size exacerbates disadvantages for boarders, while later birth order intensifies weaknesses for non-boarders. Mechanisms demonstrate that inter-generational resource allocation, particularly reduced parental economic investments and emotional engagement, rather than sibling cooperation surplus, drives these outcomes. By integrating sibling size, gender, and birth order into a unified framework and employing internationally validated measures of non-cognitive development, this study advances the understanding of sibling effects and reveals that resource dilution dominates in resource-constrained settings. Policy implications emphasize targeted interventions to mitigate inequalities in multi-child households, optimize educational investments, and leverage sibling solidarity for equitable human capital development.