Co-developmental trajectories of emotional symptoms and peer problems from childhood to adolescence: associations with positive and negative mental health outcomes.

This study used data from the Millennium Cohort Study (MCS) to examine the co-developmental trajectories of emotional symptoms and peer problems from ages 3 to 17. A sample of 16,983 children (48.8% female, 82.4% White ethnicity) was analyzed using parallel-process latent class growth models (PP-LCGMs) to explore how emotional symptoms and peer problems evolve over time and their associations with positive and negative mental health outcomes at age 17. Five trajectory classes were identified: "Primary peer problems" class (12.2%), "Co-increasing high risk" class (4.0%), "Co-decreasing medium risk" class (7.1%), "Primary emotional symptoms" class (10.3%), and "Persistent low risk" class (66.6%). The "Persistent low risk" and "Co-decreasing medium risk" classes reported the highest levels of mental wellbeing and self-esteem, relatively high levels of self-control, and the lowest levels of psychological distress, self-harm, and suicide attempt at age 17. The "Co-increasing high risk" and "Primary emotional symptoms" classes reported the poorest outcomes. The "Primary peer problems" class fell between these classes. Findings highlight the importance of identifying heterogeneous co-developmental patterns of emotional symptoms and peer problems from childhood to adolescence and call for tailored intervention programs to reduce risk and promote long-term well-being.