Effective and efficient assessment is essential to support school improvement, the progress of individual pupils and teachers' classroom management. A group of educational psychologists used the items for measuring pupils emotional and behavioural development found in "Supporting school improvement: Emotional and behavioural development" (2001) to develop a questionnaire for use in their schools. Following the introduction of the Behaviour Questionnaire (BQ) its usefulness, ease of completion and potential as a tool to monitor intervention were evaluated. Most users found the Behaviour Questionnaire useful and easy to complete. Changes in the behaviour of pupils were identified indicating that the Behaviour Questionnaire has potential for use in monitoring and evaluating interventions.