This study examined long-term mediating effects of the "smalltalk" parenting intervention on children's effortful control at school age (7.5 years; 2016-2018). In 2010-2012, parents (96% female) of toddlers (N = 1201; aged 12-36 months; 52% female) were randomly assigned to either: standard playgroup, "smalltalk" playgroup (group-only), or "smalltalk" playgroup with additional home coaching ("smalltalk plus"). Multi-informant data indicated that "smalltalk plus" had unique indirect effects on children's effortful control, through parents' capacity to 'maintain and extend' children's focus during joint interactions. Possible mediating pathways via parent verbal responsivity, home learning activities, and descriptive language use were not supported. When parents received a structured playgroup program with additional home coaching, sustainable benefits were evident in children's self-regulation, assessed in the early school years.