This study examined bidirectional associations between mothers' depressive symptoms and children's externalizing behavior and whether they were moderated by preschool‐age effortful control and gender. Mothers and teachers reported on 224 primarily White, middle‐class children at ages 3, 5, and 10. Effortful control was assessed via behavioral battery and mother ratings. Structural equation modeling indicated that maternal depressive symptoms at child age 3 predicted more externalizing behavior at age 10 among children with low effortful control and among boys. Externalizing behavior at age 3 predicted fewer depressive symptoms at the age 10 assessments among mothers of children with high effortful control. Boys with suboptimal self‐regulation exposed to high levels of maternal depressive symptoms were at greatest risk for school‐age behavioral problems.