Koerner was educated at the Gymnasium of Krefeld, graduating in March 1960. He performed obligatory military service the following two years, beginning his studies in German and English philology, the history of art, pedagogy, and philosophy at the University of Göttingen in the summer of 1962, with the idea of becoming a high-school teacher. Three semesters later he moved to the Free University of Berlin, but also studied English literature and applied linguistics for two terms at the University of Edinburgh (1964–1965), before returning to Berlin in the summer of 1965 for his Philosophicum.