This paper presents a systematic review on published research on universal school-based relationships and sex education for children aged 4–18 years. The review excludes papers focused solely on targeted cohorts, specific content areas and approaches such as abstinence-only education. Systematic searches were conducted with 5007 papers identified and following three rounds of screening, 134 papers were included in this review. The review sought to identify the terms used to describe sex education, the content included in programs or curriculum, the approaches forming the basis for implementation, the methods used to evaluate programs including the outcomes assessed. We conclude that the terms used in the field are vast, the content varied, approaches were wide-ranging, methods numerous and claims to effectiveness fluctuated and at times contrasted. Future research should seek to identify consistency in terminology and content, identify pedagogical approaches that are fully described building on the field of expertise in education, and engage highly rigorous methods and expertise in evaluation. The field of sex education must be recognized socially and institutionally so that appropriate funding and resources can be distributed to achieve the depth and breadth of knowledge required to progress the field. The implications of this impact on children's access to and ability to develop knowledge, skills, behaviours and critical thinking about themselves and their relationships.