The impact of greening interventions in school grounds on social behavior and cognitive performance among primary school children.

Background: Green spaces have been identified as beneficial for children's mental health, as well as cognitive performance, however, less is known about the role of biodiversity within these environments. Here, we study the impact of greening schoolyards, especially with regard to biodiversity enrichment, on children's behavior, emotion recognition, cognitive performance and mental effort, and attentional bias, compared to observations in control schools. Methods: This study employs an interventional design, including two intervention and two control schools located in Belgium and the Netherlands. Data was collected from 169 children aged 7-12 years, assessing cognitive performance using a battery of cognitive tasks combined with eye tracking, as well as socio-emotional wellbeing via eye tracking and validated questionnaires. Baseline measurements were followed up every 6 months for 2 years. Findings: Selective attention in the Stroop test and mental effort, as indicated by enlarged pupil diameters during cognitive tasks, increased more over time in the intervention group compared to the control group as schoolyard greening progressed. The intervention was associated with improved scores on prosocial behavior over time. These associations were independent of sex, age, country, education level of the household, the capacity to manage household incomes, and season. Attentional bias towards the emotion of happiness using eye-tracking did not show a significant difference in changes over time between intervention and control groups. Interpretation: These findings suggest that a green, more biodiverse school environment could improve children's cognitive and emotional functioning, highlighting the importance of designing schoolyard green spaces that enhance both nature contact and biodiversity as a valuable public health initiative.