Literacy is a basic human right, essential for participation in education and employment (The Universal Declaration of Human Rights, 1948). The ultimate aim of reading is comprehension. This requires the decoding of print, as well as understanding the message the print conveys. Literacy learning begins early in life. Children need proficiency in oral language and early literacy skills prior to and during the early years of schooling to ensure successful reading acquisition and development. Accordingly, all children require support in their oral language and early literacy development, prior to and during their first year of schooling. This support is essential for the formation of a solid foundation for future academic and career success. Despite the importance of reading, international studies examining the reading achievement of children provide evidence that many fail to develop the skills they require to become skilled readers. Recent studies report that between 16% and 20% of Australian students have difficulties learning to read (Thomson, Hillman, Schmid, Rodrigues, & Fullarton, 2017; Westwood, 2001). Furthermore, in Australia, many students come from communities of significant diversity because of factors such as socio-economic differences, cultural differences, and linguistic backgrounds. Due to the high prevalence of reading difficulties in diverse populations and their long-term impacts on society, independent reviews, government initiatives, and political agendas have been put in place in an attempt to address these difficulties. Improving the reading skills of diverse populations requires a sophisticated approach that takes into account that measuring and conceptualising disadvantage must consider a student’s development within their social and physical environments, as well as the impact of individual, family, and community factors. International research has provided evidence to support positive improvements for at-risk students through school-based reading interventions centred within Response to Intervention (RtI) frameworks. RtI is a framework used by schools to provide intervention to students through a tiered system of progressively intensive support. Clinicians and educators in Australian settings rely on international research that neither mirrors the service delivery models nor the cultural and linguistic diversity of the local setting. Therefore, the established school-based principles of intervention from overseas research, including the targets, dosage, intensity, and assessments require further longitudinal investigation in an Australian setting. In an attempt to address this issue, the effectiveness of a classroom-based oral language and early literacy intervention, PrepSTART, developed by speech-language pathologists (SLP) and implemented by teachers and teacher aides in the first formal year of schooling (known as ‘prep’ in some parts of Australia). The studies in this thesis include an examination of appropriate measurement; evaluation of PrepSTART, and long-term follow up for students from diverse cultural, linguistic, and socioeconomic backgrounds involved in the evaluation.