The objective of this study was to examine associations between trajectories of childhood neighbourhood social cohesion and adolescent mental health and behaviour.

This study used data from the National Longitudinal Survey of Children and Youth, a nationally representative sample of Canadian children. The sample included 5577 children aged 0–3 years in 1994–1995, prospectively followed until age 12–15 years. Parental perceived neighbourhood cohesion was assessed every 2 years. Latent growth class modelling was used to identify trajectories of neighbourhood cohesion. Mental health and behavioural outcomes were self-reported at age 12–15 years. Logistic regression was used to examine associations between neighbourhood cohesion trajectories and outcomes, adjusting for potential confounders.

Five distinct trajectories were identified: ‘stable low’ (4.2%); ‘moderate increasing’ (9.1%); ‘stable moderate’ (68.5%); ‘high falling’ (8.9%); and ‘stable high’ (9.3%). Relative to those living in stable moderately cohesive neighbourhoods, those in stable low cohesive neighbourhoods were more likely to experience symptoms of anxiety/depression [odds ratio (OR) = 1.73, 95% confidence interval (CI) 1.04–2.90] and engage in indirect aggression (OR = 1.62, 95% CI 1.07–2.45). Those with improvements in neighbourhood cohesion had significantly lower odds of hyperactivity (OR = 0.67, 95% CI 0.46–0.98) and indirect aggression (OR = 0.69, 95% CI 0.49–0.96). In contrast, those with a decline in neighbourhood cohesion had increased odds of hyperactivity (OR = 1.67, 95% CI 1.21–2.29). Those in highly cohesive neighbourhoods in early childhood were more likely to engage in prosocial behaviour (‘high falling’: OR = 1.93, 95% CI 1.38–2.69; ‘stable high’: OR = 1.89, 95% CI 1.35–2.63).

These results suggest that neighbourhood cohesion in childhood may have time-sensitive effects on several domains of adolescent mental health and behaviour.