Despite ongoing disagreement about what kinds of evidence are most valuable to education, there continues to be an increasing push to make a narrow group of scientific methodologies the basis of educational policy and practice. This has created a growth in the use of randomised control trials (RCTs), which are considered an exemplary example of scientifically rigorous research design. Yet despite the increase in both the prevalence and status of RCTs, this article will argue that the ethics informing this research orientation remains underdeveloped, with the specific need for an agenda that grapples with assent in RCTs in both a philosophical and a methodological way. As a corrective to this, we engage with Biesta's observation of a lack of explicit engagement with the values informing our decisions about the direction of education practice. We begin by examining assent in existing education research literature, focusing on some of the ways that qualitative and praxis-oriented researchers have grappled with the complexity of assent in research projects involving children and young people in schools. We then consider analogous debates concerning assent in fields such as bioethics and biomedicine, given the established nature of bioethics as a discipline. Finally, we turn our attention to developing an agenda that can work towards a consideration of assent in RCTs in education research, with the purpose of making transparent some of the ethical concerns that warrant attention in the design and conduct of RCT research studies in education.