In this paper the tension between qualification, socialisation and subjectification – as defined by Biesta - is discussed in relation to teachers’ reflection about Education for Sustainable Development (ESD). The point of departure is the discussions among teachers from an ESD certificated school (upper secondary), reflecting about their teaching. The desire to empower critical thinking as a key competence of the students is revealed as an important educational goal. How is critical thinking discussed in relation to qualification, socialisation and subjectification in ESD? What conflicts emerge? In educational research as well as in policy documents there is an ambition to put forward the complex and conflicting views of sustainable questions. Pluralism is put forward as a means of handling these ‘competing visions of the truth’. What opportunities for students to develop their thoughts and ideas of sustainable issues (subjectification), do teachers formulate within the frame of formal education (qualification and socialisation)? The paper concludes with a discussion about the relevance this tension has in an educational context from a pluralistic approach of sustainability.