The inclusion of a rapport phase with children in investigative interviews is considered best practice as research shows that this can improve the quality of information provided. However, the phenomenon of `psychological rapport', as demonstrated in a person's behaviour, is less understood. Specifically, how do practitioners build rapport with children in the rapport phase? The aim of this paper is to provide information on the methods used by practitioners for building rapport with children, with an explanation of how they may influence communication. Nineteen Scottish practitioners (police officers and social workers) were interviewed about their experiences and approach to rapport building with children in investigative interviews. These interviews were qualitatively analysed using a grounded theory approach and produced a model for the relationship between psychological rapport and children's communication. According to this group of practitioners, rapport building acts as a `communication tool' and is approached using three main strategies. These strategies involve using rapport to assess the child, adjust interview approach based on the assessment, and produce a change in the child's psychological state that facilitates communication. These findings have established practitioner understanding of rapport building and highlighted a number of areas that require further research.