Studies with preschool children have shown significant links between children's executive function (EF) and theory of mind (ToM), but few studies have examined these associations in primary school children. To address this gap, we designed a three-wave cross-lagged longitudinal study in which we followed a group of 113 children (61 boys) across three time points from age 9.5-10.5years (mean age at Time 1=112.3months, SD=4.18; mean age at Time 2=118.3months, SD=4.15; mean age at Time 3=124.7months, SD=4.06). At each time point, we measured EF (working memory and inhibitory control), ToM, and language. Our analyses showed (a) moderate rank-order stability of individual differences in both EF and ToM and (b) growth in ToM task performance across time. Cross-lagged longitudinal analyses revealed an asymmetric developmental relation between ToM and working memory. Early working memory predicted later ToM but not vice versa. Our results suggest a specific role for working memory in the ongoing development of ToM in middle childhood.