[3] Duncker was briefly a pupil at the Köllnisches Gymnasium in Berlin, but his stepfather decided that a career in business would suit him better than an academic one, and he was switched to a commercial school recently established by Karl Spazier [de] and a Dr Schulze.

On completion of his training period Voß wrote that Duncker had applied himself to his work and to his learning "with demonstrable care and fidelity" ("mit der bewiesenen Treue und Aufmerksamkeit").

Nicolai came down in support of Duncker who was left in post, to manage the business through what proved to be an exceptionally difficult couple of years for those seeking to live through commerce.

Berlin was occupied by French troops between October 1806 and December 1808,[5] while intensified fighting persisted in Silesia and East Prussia, where the king had been obliged to move with his court and government following military defeat in 1806. International trade was also inhibited by the blockade of the Prussian ports imposed by the British navy in response to Emperor Napoleon's so-called Continental System.

[1] Despite all this, by 1808 Duncker had managed to clear all the debts of the firm, and the withdrawal of French troops from Berlin at the end of the year offered the possibility of slightly less troubled times ahead.

[1] In broad terms, Duncker's strategy followed the path established by Heinrich Frölich, while displaying a keen sensitivity to evolving trends in taste and attitude.

He was endlessly attentive to the publication of Karl Friedrich Becker's nine volume "World History for Children and Teachers" ("Weltgeschichte für Kinder und Kinderlehrer").

Becker died in 1805, but the work was repeatedly expanded and updated by other historians, described later by his son as "excellently selected editors" ("vortrefflich gewählte Bearbeiter"): by 1867 it had reached 20 volumes.