Applied Behaviour Analysis (ABA) has its foundations in the science of behaviour and is used effectively to address socially important behaviours, such as the education of children with Autism Spectrum Disorders (ASD) (Baer, Wolf & Risley, 1968). The evidence to support the use of ABA in behaviourally based interventions with ASD in education settings is growing (Eldevik et al., 2006; Kovshoff et al., 2011; Grindle, 2012; Kasari & Smith, 2013; Peters-Scheffer et al., 2013; Foran et al., 2015; Lambert-Lee et al., 2015 and Pitts et al., 2019). This thesis focuses on the provision of ABA-based education for young children with Autism Spectrum Disorders (ASD) in a mainstream school unit in Wales. More specifically, the research explores some of the factors that influence the decisions that parents and providers make when they choose and commission ABA-based interventions. The original plan was to conduct mixed methods research to explore the variables around setting up an ABA unit in a mainstream school, and to evaluate the outcomes of the children involved in that project. For reasons that will be explored in more detail in this dissertation, the ABA classroom in the school was not established in the research time frame (from 2015 to 2018). The focus of the dissertation changed to understand four areas: Why parents want ABA for their children; what the school thinks about ABA; how the parents’ and providers’ views about ABA are informed by evidence, and what the barriers to implementing ABA in a mainstream school are. Using a qualitative research design a sample of parents and providers from a school setting, including the local education authority (stakeholders) were interviewed to explore their understanding of ABA as an intervention for ASD, and how it could be implemented in a mainstream school. The motivations of the stakeholders to choose and implement ABA, and the barriers that were perceived as a result of that process are analysed in this dissertation. Chapter 1 reviews the evidence in the literature that relate to the thesis, and Chapter 2 presents the methodology used to gather the evidence. Chapters 3 and 4 analyse and discuss the data gathered from the stakeholders. Chapter 3 focuses on the stakeholders’ motivations behind their decisions to choose ABA, and Chapter 4 examines the data on the barriers to implementing ABA-based interventions in the mainstream school. Lastly, Chapter 5 presents an overall discussion of the thesis and outlines implications for this research within the field of ABA and makes recommendations for further study.