From a column in the Star Tribune about the origins of assorted (non Classical) words:

Word: Dunce. From: John Duns Scotus (c.1266-1308). Derivation: The followers of Scotus, a theologian and philosopher, were called "duncemen," after his birthplace (Duns, Scotland) and middle name. They opposed the revival of Classical studies in the Renaissance, and thus the word "dunce" came to mean an uneducated person.

... hmmm ... I've never heard about this 'opposition to Classical studies' thing ... I also never bought into the Straight Dope's thing on the origin of the dunce cap ...