Investing in girls’ and women's education can transform the experiences of individuals, as well as shape communities into the future. Girls who are given opportunities to receive an education are more likely to lead productive lives, participate in decision making processes, and shape the trajectories of others. The work of the ASEAN-UK SAGE programme reflects an overarching aim to better understand the challenges facing different types of girls and women in the Association of Southeast Asian Nations (ASEAN) region, identify promising practices that can support girls and women, and create tangible recommendations for those responsible for supporting girls and women's educational trajectories across the lifespan. Data shows concerning levels of children and youth not completing lower-secondary and upper-secondary schooling. While primary completion rates hover around 80% in Cambodia, Myanmar, Lao PDR and Timor-Leste, rates fall to just over 50% in lower-secondary. While half of students complete upper secondary in Timor-Leste, only 20-30% in Cambodia, Myanmar and Lao PDR do. Even though girls now remain in the education system for longer, they are less likely to be in employment, further education, or training in the ASEAN region. From the age of 15, women also earn less than men in the seven ASEAN member states for which data are available, impacting on household financial stability and resiliency. Girls also face ongoing risks of forced and early marriage, period poverty, violence and trafficking, female genital mutilation, adolescent pregnancy, and sex-selection before birth. Given the gains made by girls in the region, and the importance of acknowledging that other gender groups can also be vulnerable within ASEAN education systems, this report focuses on two broad groups: out-of-school girls, and children and youth from marginalised groups. Understanding ways to better support the complex needs of these different groups is a key focus of the SAGE initiative. As part of a three-part series examining ways to support girls, women, and other vulnerable and marginalised populations, this report focuses on understanding the current challenges ASEAN countries face in supporting out-of-schoolgirls, and children and youth from marginalised groups and examines effective practices for supporting these underrepresented and hard to reach populations.