2020, The Author(s). School staff have a unique opportunity to detect and respond to mental health issues including self-harm and suicidal behaviour in adolescents. There is limited knowledge about how these incidents are managed in schools. This study aims to understand the incidence rates, perceived severity and management of self-harm and suicidal behaviour incidents by schools. A total of 1525 school incidents were analysed for rate, severity and response. Pearson's χ2 test was used to understand incident rates of self-harm and suicidal behaviours compared to all other incidents, and if incident category was related to emergency service involvement. A Kruskal-Wallis ANOVA analysed differences in severity ratings for incidents, and relative risk ratios determined the probability that first responder services will be engaged in self-harm and suicidal behaviour incidents. Self-harm and suicidal behaviour incidents (n = 77) accounted for 5.05% of all incidents and were more likely to be rated highly severe compared to other incidents. Incidents of self-harm and suicidal behaviours were 1.43 times more likely to have police involvement and 8.37 times more likely to have ambulance involvement compared to other incidents that caused harm to students, staff or property including welfare and violence incidents. The findings highlight the severity of reportable self-harm and suicidal behaviour incidents as they required an emergency response. We discuss the potential missed opportunity for early intervention by school staff and services, which may hinder future disclosure or help-seeking by at-risk young people. Training of school staff may provide knowledge and confidence to respond appropriately to self-harm and suicidal behaviour incidents and prevent escalation requiring emergency intervention.