The subject of environmental science (ES) was introduced into Bhutanese schools to educate students about sustainable environmental conservation. This study aims to answer the research question: What are the impacts of studying ES on Bhutanese students for environmental sustainability? The study employed mixed methods to draw data from interviews with six principals, 14 teachers and 189 students, and surveys with 14 teachers and 563 students from six secondary schools. Participants indicated the development of students' Gross National Happiness value of sustainable environmental and socioeconomic development. However, an anthropocentric perspective appeared to be dominant among participants, suggesting a need to develop ecocentric worldviews to support sustainability. Most students noted their changed behaviours, development of optimism, stewardship and agency towards ecological sustainability from studying ES. To prepare students to take action to address sustainability issues, teachers could leverage students' optimism, agency and stewardship through action-oriented approaches to teaching ES.