There’s a story about an art teacher that split their class 
  in half. They told one half of the students that they’d be 
  graded based on a single piece of work, and the other half 
  that they would be graded on the quantity of work produced.

Does anyone know of an actual event where this happened, or is it apocryphal?

(I don't disagree with the premise, I'm just curious about its basis)