 After failing to find a university position better than that of Privatdozent, he accepted an offer to teach at his old school, the Duisburg Gymnasium. He taught there from 1858–1862. He gave classes on Greek, Latin, German and philosophy. He was also busy outside the classroom writing reports for the school authorities and participating in politics as an elector. He wrote many articles for Karl Schmid’s encyclopedia of pedagogy during this time (Lange 1869–75). This was the period when Lange really became a political activist. He participated in the organization of the new consumer cooperatives meant to help the working class avoid exploitation by merchant traders—the traders sold low-quality goods at high prices and encouraged indebtedness. He was involved with the liberal, nationalist society, the Deutsche Nationalverein (whose members were later to form a similarly motivated political party, the Deutsche Fortschrittspartei) attempting to achieve German unification.