The current generation of young people is less mentally healthy than previous generations. Rates of bullying and other forms of violence remain at worrying high levels in the UK and elsewhere. Use of alcohol, tobacco and other substances has seen recent decline in high-income countries, including the UK. However, there is evidence that this is now levelling off and, for some substances, increasing again. Young people's sexual health is improving globally, but in the UK young people report high levels of risk behaviours and adverse sexual health outcomes. Young people, particularly in high-income countries, tend to have poor diets and engage in insufficient physical activity, with increasing rates of obesity.

Schools are not the only cause of these problems, but they do play an important role. Drawing on qualitative research, I have described the ways in which schools can harm young people's health through mechanisms involving educational disengagement, lack of belonging in school community, and fear and anxiety. Statistical evidence from different kinds of study supports the view that schools have an impact on risk behaviours and health outcomes via these mechanisms. The best evidence is from longitudinal studies that track students over time and examine statistical associations between various school-level characteristics and students’ health outcomes or risk behaviours, adjusting for potential confounders. These studies suggest that within education systems, some schools do a better job than others of protecting their students and avoiding the three toxic mechanisms.