Mental health spillovers in primary schools

In this paper we use extensive Danish register data to study peer effects from students with mental health problems. In our analysis mental health problems are defined from diagnosis in hospital registers. We follow classes from 1st to 6th grade (most students are reshuffled in grade 7) between 2007 and 2013 and study mental health trajectories of incumbent students when receiving a new student with mental health problems. We use a time to event design, controlling for individual and grade fixed effects and using never treated classes as the control group. We condition on students being observed from grade 1 until treatment and follow them after treatment irrespectively of the school or class they attend. Following the new difference-in-differences literature, we produce estimates that are robust to heterogeneity across cohorts and grades. As additional robustness check, we compare against classes that receive a new student without a mental health problem and produce results adjusting for changes in diagnoses trends. We find that incumbent students’ mental health is affected by receiving a new student with mental health problems, an effect that is larger when first exposure occurs by grade 6. These effects are long-lasting irrespective of the gender of the mover and of the gender of the incumbent student. When breaking down treaters by type of diagnosis we find evidence of treaters with ADHD and autism causing exposed students to be more likely to be diagnosed with depression and anxiety.