A teacher proposed that the refugee boy should apply for the Gymnasium. Köhler took his "Abitur" in 1963. After a two-year military service at a Panzergrenadier battalion in Ellwangen, he left the Bundeswehr as reserve officer. He studied and finally earned a doctorate in economics and political sciences from University of Tübingen. There, he was a scientific research assistant at the Institute for Applied Economic Research from 1969 to 1976.