Research has demonstrated that young children with problem behaviours are at risk of developing anti-social attitudes and behaviours that will follow them throughout their schooling and into their adult years. Effective intervention can alter this developmental trajectory. This needs to include the involvement of early childhood teachers because even early childhood teachers report that children’s inappropriate behaviours are one of the major challenges they face in the classroom. However, many early childhood teachers are unaware of the evidence-based practices that have the potential to decrease problem behaviour. The aim of this study was to uncover the current behaviour management strategies used by teachers at a preschool and to examine the effects of training early childhood teachers in the effective use positive teaching strategies to increase appropriate behaviour and decrease inappropriate behaviour in three and a half to five year old children. A variety of methodologies were employed in this study including direct observations, use of the Canterbury Social Development Scale and reflective teacher questionnaires. The study found that teachers’ initial understandings of simple strategies such as contingent praise and attention were limited and that they would benefit from an in-service training programme. After implementing the training it was found that all teachers increased their ordinary and descriptive praise statements and they increased in their contingent responses following requests. These changes were maintained above Baseline levels for all teachers. The number of discouragements remained consistent across all phases. An increase in teacher praise was accompanied by an increase in appropriate child behaviour and a decrease in inappropriate child behaviour. Though this study was successful in changing both teacher and child behaviour it also raised a number of important implications, including issues of the maintenance of behaviour change and the importance of feedback and the use of one-on-one coaching when conducting professional development in behaviour management at the preschool level.