Internalising Symptoms and Developmental Milestones in Adolescents: The Moderating Roles of Parental and Peer Support

Abstract

Objective: Internalising symptoms, developmental milestones achievement, and the differential buffering role of parental and peer support are critical domains for adolescents’ future health and development; however, no prior research has considered these variables jointly or in a clinical sample. To fill these gaps, the present study aimed to investigate the relationship between internalising symptoms, developmental milestones achievement, and the moderating roles of parental and peer support in clinically referred youth. Method: The current research employed a cross-sectional design with data of the first wave of the Dutch longitudinal APOLO project. The sample included 182 adolescents (M = 15.5 years; 73.3% female; 26.2% male) referred to one of two Dutch mental health care clinics. They completed self-report measures on internalising symptoms, developmental milestones achievement, and perceived quality of the relationship to a parent and peer. Results: Youth with higher levels of internalising symptoms reported lower levels of developmental milestones achievement. No moderation of either parental or peer support was found. Still, more parental and especially peer support were related to higher developmental milestones achievement, highlighting their role as general protective factors for developmental milestones achievement. Conclusion: Consistent with systems and transactional models of development, these findings suggest the inclusion of milestone-related competencies alongside parental and peer support interventions in current treatments for youth with internalising symptoms to promote positive development.