Effects of a Digital Parent–Child Single-Session Growth Mindset Intervention on Adolescent Depression and Anxiety Symptoms: A Three-Arm Waitlist Randomized Controlled Trial

Adolescent depression and anxiety are prevalent, yet brief and scalable parent–child digital interventions remain understudied. This study evaluated the effects of a digital parent–child single-session growth mindset intervention targeting beliefs about intelligence, failure, and emotion on adolescent internalizing of symptoms. In a three-arm waitlist cluster randomized controlled trial, 390 parent–child dyads from seven secondary schools in Hong Kong were assigned to a parent–child intervention group, a child-only intervention group, or a waitlist control group. Students were assessed at baseline, 2 weeks, and 3 months, and parents at baseline and 3 months. Cluster-adjusted generalized estimating equations were used for intention-to-treat analyses. A significant time-by-group interaction was observed for child-reported depression, whereas the interaction effects for other outcomes were non-significant. However, cluster-adjusted baseline differences across groups limited attribution of changes in depression to intervention effects. Relative to controls, the parent–child intervention descriptively showed short-term improvement in hopelessness and sustained gains in child-reported parent–child relationships over 3 months. Moderation analyses suggested clearer short-term benefits among adolescents with higher baseline symptoms and among girls. Overall, the PC-SMILE intervention in this study did not show statistically significant effect on reducing internalizing symptoms. Improvement on intervention design and implementation would benefit further refinement of brief, scalable parent–child digital interventions. Trial registration: ClinicalTrials.gov NCT05493865.