1. BACKGROUND TreeHouse is a school for children with severe autism, based in central London. The TreeHouse curriculum is based on Applied Behaviour Analysis (ABA), an intensive, highly structured teaching method based initially on a 1:1 teacher/pupil ratio. In common with all severely autistic children, there are some pupils at TreeHouse who display extreme challenging behaviours such as screaming, spitting, vomiting and aggression towards themselves and others. This can be frightening and upsetting, both to adults and children, causes a barrier to the children's learning, and compounds their isolation and social exclusion. A key part of their education is to reduce these negative, challenging behaviours and replace them with positive, appropriate ones such as being calm, engaging and interacting with others, as well as enjoying constructive social and educational activities. TreeHouse's previous approach was to integrate the children with challenging behaviours in their age-appropriate class. 2. NOMINATION A new strategy has been developed to establish a dedicated 'high support class' solely for these children, currently numbering 5. The 1:1 teacher:pupil ratio has been increased to one class teacher and six assistant teachers, and a high-tech surveillance system has been introduced to monitor and analyse behaviours and for training purposes. A non-intrusive camera records the activities in class, transmitting to a monitor in the behaviour analysts' office. This enables the team to watch the class in progress non-invasively, and for the behaviours to be recorded and studied to examine the causes of the challenging behaviours when they occur. This is supplemented by taking baseline measurements of problem behaviours and collecting antecedent-behaviour-consequence data. This information is entered into a software programme that graphs the data in terms of common antecedents and consequences as percentages. Challenging behaviours that result in injuries to the children themselves, other children or to staff are recorded electronically and stored in a database for review by the School Management Team. 3. OUTCOMES The high support class has enabled the behaviour analysis team and teachers to test a range of strategies to address challenging behaviours, and record the results to analyse and evaluate the children's responses. The successful strategies are then further developed and improved to ensure their continued efficacy. The interventions that have been employed have been phenomenally successful in replacing negative behaviours with positive ones. Indeed, it is fair to say that were it not for the intervention offered at TreeHouse, many of its pupils, certainly all who display these challenging behaviours, would be in full time residential care. TreeHouse has enabled families to remain together. The high support class has provided training opportunities for staff in the necessary skills and competencies to work with children who have greater support needs. This learning is being shared with TreeHouse staff and parents who deal with the pupils each day, and with staff from external providers of education to autistic children who are struggling to cope with the burden of children with challenging behaviours in their settings. Susan Beck