In Australia, junior high school students expelled from mainstream schools for disruptive behaviour, are typically diverted to Behavioural Schools for continuing education. These schools are part of the public education system. Behavioural Schools are stand-alone alternative education settings with small numbers, high teacher to student ratios and correspondence-style learning, conducted within a strict behavioural modification framework. Typically, students at the Behavioural School range from 12-15 years of age and have mental health problems at the severe end of the spectrum. Despite the societal importance of addressing the mental health issues of these students, a paucity of robust literature exists on effective group treatments for this population. This quasi-experimental study (N = 8) attempts to address this gap by providing quantitative and qualitative information on a 16-week CBT-based aggression management training for Behavioural School students. A repeated measures design, utilising student, teacher and parent input, enabled comparison of the following dependent variables: DSM-IV diagnoses, attendance, suspensions, withdrawals, disruptive behaviours and peer relations. Results revealed that over the period of training students received fewer suspensions and withdrawals and the severity of their conduct problems lessened. Qualitative analysis of teacher focus groups affirmed the value of psychological intervention for these students.