Education for sustainability (ES)  is aimed at developing competencies, skills, values ​​and attitudes that enable citizens to lead healthy and fulfilled lives and empower them to reflect on their own behaviors, actions and responses while taking into account current and future social, cultural, economic and environmental factors, making informed decisions and responding to challenges at the local and global level (UNESCO, 2016, pp. 4). People who act according to the aforementioned guidelines are referred to in recent literature as "sustainability citizens" (Wals, 2015; Wals and Lenglet, 2016), and the main goal of education for sustainability is educating such future members of our society - "sustainably" accountable and active citizens (UNESCO, 2017). Education for sustainability is competence-based transformative education focused on developing key cross-cutting competencies needed for an individual to transform their lifestyle and contribute to social transformation towards sustainability.

One of the main priorities of education for sustainability is the education of student teachers, as they are often referred to as the most important actors of change and promotion of sustainable development (UNESCO, 2015; 2017). In considering the role of teachers in the context of sustainable development, the question arises as to what competences teachers should have in order to successfully implement education for sustainability in their practice. This challenge, as well as the need to respond to these and similar issues, was further emphasized by UNESCO through the Global Action Program (GAP) aimed at enhancing the multiple activities and experiences of the UN's "Decade of Education for Sustainable Development" (UNESCO, 2014). The GAP seeks to make a significant contribution to achieving sustainable development goals by redirecting education and learning so that everyone has the opportunity to acquire knowledge, skills, attitudes and values ​​that strengthen them to contribute to sustainable development. To provide strategic focus and encourage the commitment of all stakeholders, five priority action areas have been identified through the Global Sustainable Development Action Program, one of which is directed at (future) teachers and teachers, i.e. "capacity building of teachers, teachers and educators "in education for sustainable development (UNESCO, 2014).

The role of developing teacher sustainability competences is twofold. First and foremost, in order to have capacity to integrate and successfully facilitate ES, teachers must be sustainability citizens with developed key sustainability competences, including knowledge, skills, attitudes, values, motivation, commitment and behaviours toward sustainability. On the other hand, teachers should adopt specific competences related to the ability to help students develop sustainability competences through a number of innovative learning and teaching practices. These elements of sustainability competence for teachers are explained through several conceptual models, such as the Curriculum, Sustainable Development, Competences, Teacher Training (CSCT) model, (Sleurs, 2008), Learning for the Future Model:  The Competencies in Education for Sustainable Development (UNECE) model, UNECE, 2012), KOM-BiNE model (Rauch and Steiner, 2013) the approach of Bertschy et al. (2013). Within the aforementioned models, teachers are not only seen as professionals, but as individuals with social responsibility, which requires them to be highly qualified.

In order to achieve the goals of sustainable development, competent and committed actors are needed – (future) teachers who will have not only the desire but also the ability to contribute to change in different educational sectors. To achieve this, these actors should have the opportunity to develop the necessary competencies along their educational path.

Mixed-method research on the contribution of higher education in developing sustainability competences of student teachers is part of a larger, mixed-method project “Formal Education in Service of Sustainable Development”, 5 years long research project funded by Croatian Science Foundation (2018-2023). This research is a pilot study that investigates student teachers' perceptions of the role their higher education had in development of their sustainability competencies. Research question, the purpose of the pilot study was to determent differences in student teachers' perception of to what extent their higher education: (I) contributed to and (II) should have contributed to the development of their sustainability competencies. In addition, respondents answered two open questions: they described what they think about promoting sustainable development in their future work as a teacher, and their recommendations for improving education in order to increase the sustainability competence of future teachers. The study involved 152 student teachers at the University of Rijeka, Faculty of Humanities and Social Sciences (average age of participants was 22,95 (SD=1,24). A questionnaire was developed for the purpose of the quantitative part of the research. List of derived competencies was generated from the Handbook for SE (Education and Teacher Training Agency, 2011, pp. 23) based on some aspects from UNESCO Guidelines (2015, 2017) and they are the following: critical thinking skills and the ability to ask analytical questions, the ability and courage to overcome obstacles and solve problems, thinking holistically and interdisciplinary – the ability to connect knowledge, thinking creatively- thinking outside of the box, challenging stereotypes and being oriented towards the future, the ability to manage changes which presupposes the ability to define problems, the ability to apply knowledge in real life situations, the ability to handle crises and risks, decision-making in uncertain circumstances, the ability to express oneself (viewpoints, interests, aspirations, principles) and to communicate, the ability to overcome stress, the ability to cooperate and work in teams, readiness to accept division of tasks and take responsibility, participation in the democratic decision-making, the ability to identify social partners and their interests, and negotiation skills and the ability to reach a consensus. The task for the student teachers was to assess the contribution of their university education in development of sustainability competencies and estimates to what extent university education should contribute to the development of sustainability competence on a Likert type scale (where 1 means completely disagree and 5 fully agree).

Quantitative results indicate a great discrepancy in the student teachers' perception of expected and obtained contribution of education in development of their sustainability competencies. Student teachers estimate that their education significantly less contributed to the development of sustainability competences than needed. Also, the insight into qualitative data has revealed that student teachers recognize the need to promote sustainability in their future work, and that teacher education should empower them to be ready to respond to this challenge, but there is also an attitude of student teachers that teaching for sustainability is not their obligations, that they will not have enough time doe to primary subject they will taught, and education on sustainability should be taught in other subject (geography, biology etc.). The results obtained in this research clearly reflect the fact that more emphasis should be placed on competence-based education within the existing teacher education curriculum. The findings are in line in work of Barth and Rieckmann (2016) who warn that in education research analyses focus on potential solutions for integrating education for sustainable development into study programs and colleges, while lacking research focusing on educational outcomes, which would offer answers to questions what student teachers are really learning, and which competencies are acquired in the context of education for sustainability. There remains a large research space for the operationalization of competencies and the development of instruments to monitor and evaluate the development of sustainability competencies of student teachers (Wiek et al., 2016). This is not surprising since there are still no clear directives for the universal teacher education in the context of education for sustainability (Wolff et al., 2017), and in most of the countries teacher education for sustainability remains on the individual efforts of enthusiastic individuals (Green et al., 2016).

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