Why does "sophomore" refer to a second-year student?

Solution 1:

The website Straight Dope talks about sophomore by saying:

Though the first part does come from the Greek word sophos ("wise"), there is no direct relation to the Greek word for "foolish" as is commonly believed. In truth, sophomore is a variation of sophist, a word that has a long and twisted history in itself.

it goes on to say:

Originally, a sophist (Greek sophistes) was a man who had achieved wisdom. The sophist Protagoras is said to have been the first professional teacher, charging only what his students thought he had earned. He, and many sophists who came after him, were serious thinkers but not on the level of, say, Socrates. Later, professional teachers in ancient Greece became generally known as sophists, but many of these were more pretenders to wisdom than truly wise. These guys were the original insufferable know-it-alls.

This aligns with what Random House wrote when sophomore was listed as it's Word of the Day:

In Ancient Greece, the Sophists were initially a class of professional teachers who gave instruction in various fields. The word eventually took on a derogatory sense and was applied to someone of this class who, while professing to teach skill in reasoning, was more concerned with ingenuity than with soundness of argument.