There is a growing recognition of the importance of education for social emotional learning (SEL). There is a limited understanding of SEL of children in the Global South despite the growing interest, for example, in India, SEL has been emphasised in the national educational policy and by several large-scale interventions, notably the Happiness Curriculum which is being implemented across more than 35,000 public schools in two states. This explanatory mixed methods study, explores how the Happiness Curriculum impacts children’s SEL and their relations with other students, teachers, and the wider community in one of the states (Uttarakhand). Furthermore, it also explores the role of various components embedded within the intervention including curricula, classroom pedagogy, contemplative and reflective practices and project-based learning. The study probabilistically samples 50 schools and uses teacher and student surveys, contextualized SEL measures, focus group discussions and photovoice. The findings will help build an understanding of SEL development in Indian contexts, the impact of a large-scale intervention, and processes (both pedagogical and systemic) that underpin the successful implementation of the intervention. The findings will be valuable to researchers, practitioners and policymakers especially as the Happiness Curriculum and other similar interventions are scaled up across the Global South.