Parent and child physiological reactivity as moderator of a proof-of-principle randomized microtrial parenting intervention

Parenting interventions can improve child adjustment, yet benefits vary. This proof-of-principle microtrial tested whether parents' and children's physiological activation moderated a brief positive feedback intervention. Participants were 101 Dutch parent-child dyads (Mage = 4.6 years, 56% boys; 97% White) randomized to feedback (n = 51) or control (n = 50). Data were collected between October 2022 and February 2025. Parenting and child behavior were coded from interaction tasks; reactivity was indexed by heart rate residualized for baseline during interaction episodes. The intervention increased positive and reduced negative parenting, particularly among reactive parents. More reactive children in the intervention group showed higher positive and lower negative behavior at posttest than controls. Tentative evidence suggested aligned parent-child susceptibility ("dual-susceptibility"). Findings warrant replication in larger preregistered trials with longer follow-up.Parenting programs can support children's behavior and well-being, but families do not always benefit equally. This study examined whether parents' and children's physical responses to stress or excitement-such as how quickly their heart beats or how strongly they react in emotional situations-influence how well they respond to a brief positive feedback exercise. We worked with 101 parents and their 4- to 6-year-old children, who were randomly assigned to receive the feedback or not. Parenting and child behavior were observed during structured play, and these physical reactions were measured using a wristband heart rate sensor. The feedback improved parenting and child behavior, especially for parents and children who tend to react more strongly in emotional or stressful situations. There were also early signs that when both parent and child are highly reactive, they may benefit most. These findings show that how strongly parents and children physically respond to situations can shape who responds best to parenting support.