This paper considers the role played by universal, school-based social and emotional learning (SEL) programmes in addressing the mental health needs of children and young people. Theory and research in the field are discussed. Particular attention is paid to the social and emotional aspects of learning (SEAL) programme in England, a flagship National Strategy under the New Labour government whose outcomes were mixed. We examine the findings of the various evaluations of SEAL and consider what learning can be taken forward to inform future attempts to prevent emotional and behavioural problems in school settings. Recommendations include proper trialling of SEL initiatives before they are brought to scale, the use of research to inform and improve programme design, the need to temper expectations, and the importance of educating implementers about the importance of implementation quality.