This multi-method multi-trait study examined moderators and mediators of change in the context of a parenting intervention. Low-income, diverse mothers of toddlers (average age 30 months; N = 186, 90 girls) participated in a play-based intervention (Child-Oriented Play versus Play-as-Usual) aimed at increasing children’s committed compliance and reducing opposition toward their mothers, observed in prohibition contexts, and at reducing mother-rated children’s behavior problems 6 months after the intervention. Mothers’ subjective sense of life satisfaction and fulfillment during the intervention and objective ratings of psychosocial functioning by clinicians, obtained in a clinical interview were posed as moderators, and mothers’ observed power-assertive discipline immediately following the intervention was modeled as a mediator of its impact. We tested moderated mediation using structural equation modeling, with all baseline scores (prior to randomization) controlled. Mothers’ subjective sense of life satisfaction moderated the impact of the intervention, but clinicians’ ratings did not. For mothers highly satisfied with their lives, participating in Child-Oriented Play group, compared to Play-as-Usual group, led to a reduction in power-assertive discipline which, in turn, led to children’s increased compliance and decreased opposition and externalizing problems. There were no effects for mothers who reported low life satisfaction. The study elucidates the causal sequence set in motion by the intervention, demonstrates the moderating role of mothers’ subjective life satisfaction, highlights limitations of clinicians’ ratings, and informs future prevention and intervention efforts to promote adaptive parenting.