The concept of sustainable development is now an imperative of modern living if we want to ensure a secure future for our children. Changes in thinking, behavior, and way of life must happen primarily at the individual level, then at the local and global levels. The responsibility for creating a society based on sustainability has been placed on teachers who need to empower children and young people to become active citizens with the knowledge, abilities, and skills to face the unknown challenges that await them. For this reason, the pilot project "Nature Heroes" was created to support primary school teachers in achieving learning content and outcomes related to sustainable development. The project involved collaboration within the school curriculum between the Children's Creative Center DOKKICA, as the project leader, and teachers and university professors, thus integrating formal and non-formal education. The project was approved by the Ministry of Science and Education of the Republic of Croatia and was implemented from November 2021 to June 2022 in collaboration with 41 schools from different parts of Croatia, involving 69 teachers and 1,037 students in project activities. The project offered support to teachers in the form of an educational and entertaining media series and didactically designed materials that, through drama exercises and techniques, encouraged students to actively learn, communicate, collaborate, generate unusual ideas and solutions, empathize, and work as a team.

The aim of this research was to determine the usefulness and applicability of the pilot project in achieving content and learning outcomes of sustainable development in lower grades of primary school. Data was collected through tools created as part of the project: activity diary, table of recorded activities, a Facebook support group for teachers: Nature Heroes - a community of teachers where teachers shared posts about successfully implemented activities, and final evaluation in the form of an online questionnaire with reflections from teachers and students. The results were analyzed using descriptive statistics and qualitative methods. A high percentage of teachers (62.2%) assessed that their participation in the project was beneficial for their personal and professional development, and that the project stimulated their creativity and innovation. Teachers reported a range of changes they observed in the behavior of their students, such as increased attention to plants and animals in their environment, cleanliness of the spaces they occupy, the importance of proper nutrition and its impact on the human body, respect for cultural and natural heritage, increased motivation for exploring and studying topics that are not directly related to the curriculum. They also noticed increased empathy, unity, peaceful conflict resolution, collaboration, respectful behavior among students, acceptance of others and differences, self-confidence, freedom of expression, participation in discussions, and tolerance.

Keywords: Sustainable development, learning outcomes, curriculum, teachers, lower grades of primary school.