Here is a summation of what is wrong with the model of jumping from one unrelated class to the next:

"Cognitive psychology has shown that the mind best understands facts when they are woven into a conceptual fabric, such as a narrative, mental map, or intuitive theory. Disconnected facts in the mind are like unlinked pages on the Web: They might as well not exist. Science has to be taught in a way that knowledge is organized, one hopes permanently, in the minds of students."

Source:
http://pinker.wjh.harvard.edu/articles/media/2005_11_16_slate.html