This study aims to establish core competencies for environmental education in elementary schools, develop its measurement tools, and explore program grouping methods. To address these goals, three research questions were posed: identifying core competency elements, determining their assessment tools, and exploring the best ways to organize environmental education programs to develop the core competencies. Using a Delphi survey and literature review, the research pinpointed core elements such as ‘autonomy’, ‘reflective ability’, ‘environmental sensitivity’, and ‘critical thinking ability’, among others. Based on these competencies, 34 assessment items were devised. To enhance these competencies, a ‘theme integration method’ was proposed, intertwining environmental education with other curriculum topics. The study emphasizes the importance of an integrated approach, ensuring students grasp environmental subjects while achieving other learning objectives. Consequently, the measurement tools and learning & teaching programs for environmental education in elementary schools presented in this study assist teachers in customizing environmental topics based on regional, school, and individual teaching goals, rooted in the intended core competencies.