This study aimed to test a four-wave sequential mediation model linking mother-child attachment to children's school readiness through child executive functioning (EF) and prosociality in toddlerhood and the preschool years. Mother-child attachment security was assessed when children (N = 255) were aged 15 months and 2 years, child EF at age 2, prosocial behavior at age 4, and finally cognitive school readiness in kindergarten (age 6). The results revealed three indirect pathways linking attachment to school readiness: one through EF only, one through prosocial behavior only, and a last pathway involving both EF and prosocial behavior serially. These findings suggest that secure attachment may equip children with both cognitive and social skills that are instrumental to their preparedness for school.