This chapter explores the configuration of interdisciplinarity in Danish upper-secondary education in the aftermaths of a reform in 2005, which introduced interdisciplinarity as a key organising principle. Focusing on the prominence of an assessment tool, Bloom's taxonomy, in the daily practices and processes of interdisciplinarity, the chapter considers the intertwinement of interdisciplinarity with recent tendencies of accountability and performance governance in education. The chapter takes its point of departure in the historical shifts from the 1960s where the introduction of interdisciplinarity in upper-secondary education was based on progressivist critiques of definite disciplinary arrangements, to the aftermaths of the 2005 reform, where interdisciplinarity was entangled with forms of governing whereby students’ learning process and performance were supposed to be made visible and accountable. Rather than constituting a clear-cut shift, however, the chapter shows that the configuration of interdisciplinary after 2005 is characterised by bringing together different rationalities of education – emphasising learning as both an open-ended, explorative process, but also as a measurable process with definite steps. It argues that this yields a performative interdisciplinarity, where teachers and students engage in performing an explicit combination of two specialised disciplines so as to make the contribution of each discipline visible and assessable.