Failure to address poor mental health during childhood and adolescence results in higher risk of suicide, substance misuse, self-harm, and lower achievement in education and employment (Richards et al., 2009). Of the psychological factors underlying mental health, it has been argued that self-regulation is central (Posner & Rothbart, 2000). The Barkley (1997) model of self-regulation is reviewed, and evidence considered that suggests it has cross-diagnostic validity. The typical developmental courses of emotion regulation and effortful control, and how these are associated with mental health, are considered in order to inform applied psychology practice with children and young people. A refinement of the Barkley model is proposed to enable the synthesis of findings from different bodies of research, and to offer a framework by which psychopathological diagnoses might be etiologically, rather than behaviourally, defined. The research study used neuropsychological and self-report measures to test whether emotion dysregulation mediated the relationship between behavioural inhibition and psychopathological symptoms in adolescents. 39 pupils, aged 10 to 16 years, completed sustained attention subtests from the Test of Everyday Attention, the Attentional Control Scale, Difficulties in Emotion Regulation Scale, the Aggression Scale and the Strengths and Difficulties Questionnaire. Adult-report versions of the Strengths and Difficulties Questionnaire were also completed by parents and teachers. Significant, positive correlations between difficulties in emotion regulation and psychopathological symptoms were observed. Significant negative correlations were observed between behavioural inhibition and psychopathological symptoms. The mediation model was supported: emotion dysregulation fully mediated the relationship between behavioural inhibition and psychopathological symptoms. The relationship of the study results to the Barkley (1997) model of self-regulation is discussed. The study findings suggest that intervention to treat or prevent the development of psychopathological symptoms in adolescents is better targeted at reducing habits of emotion dysregulation than at improving the capacity for behavioural inhibition.