Over the last 15 years, there has been an increased engagement in interdisciplinarity in the organisation of Euro-American knowledge production and education. In Denmark, interdisciplinarity has been deployed as a central organising principle in an extensive and contested reform of the Danish upper-secondary school in 2005. A key assumption in this engagement seems to be that when it comes to creating new knowledge or preparing young people for the future in what is often described as an increasingly complex world, disciplines cannot stand alone. Instead, they must be crossed, multiplied, transcended and take a secondary role in favour of the ‘in between’. Interestingly, this preoccupation with the in-between also seems to be at stake in recent debates in the social sciences. This paper will explore the preoccupation with the in-between in the Danish gymnasium and in current debates on ontology in Science and Technology Studies. The paper will show the translations of the engagement in interdisciplinarity in Danish education policies from the 1970s’ orientation towards critical theory to the current orientation towards innovation, open-endedness and an unknown future. The paper will discuss the turn to ontology in STS and its debunking of pure and stable, modern, universal categories, juxtaposing it with the occupation with the in-between in Danish education. It will show the ways in which working with the in-between in everyday school practices does not dissolve pure and stable, modern, universal categories, but rather relocates the moment of stabilization, and suggests that this relocation of stabilization might be a way of thinking about not only the practical work of interdisciplinarity, but also the practical work of doing post-structural analysis.