Are “Real class” and “Paper class” well-received pair words?
Solution 1:
Yoichi, simply to repeat what Jim explained, as the official answer:
it's common idiom to use "paper" (or "on paper") to mean: "fake".
So, you have "paper profits",
a "paper company" (you know those fake companies on an island somewhere),
a "marriage on paper only" (when you marry a Russian friend to get her passport),
and so on.
It's simply that usage.
That's all there is to it.
Note that 99% of the time when you (Yoichi) post here an unusual usage, it's actually just because the English writer is an idiot :) Incredibly in this case, it's "all correct". :)
Additionally Jeremy very astutely points out that when you make a new coinage, it's often appropriate to indicate that with " airquotes ".
For example, well established terms are cloud computing, cloud storage, cloud backup. If I started talking about "cloud funding" it might be nice to indicate it that way, with airquotes. Doing so, I explicitly point out that I am making an analogy to the similar well-known phrases.
Solution 2:
I can see this coming from the principle of signaling unusual usage as referenced in the Chicago Manual of Style on this Wikipedia page. "Paper class" is unusual usage, so quoting is appropriate. Using real classes, does not need to be quoted, however, even though "paper class" is quoted since it is not an unusual usage of the language.
Solution 3:
Google n gram so far as I can see on my first time using it does not show 'paper class' as a word, but does show the pair of words 'paper class' appearing as you say.
Googling 'paper versus real' shows many cases where paper is used as a contrast to real, meaning inauthentic, or not to be trusted. When I read the first article cited I immediately understood that paper classes were ones where the students did not have to do any work, but would have all the right paperwork for the course to prove on paper that they were full time students maintaining the required grades to be collegiate athletes. I had not seen the term before. 'Real classes' seems to be the best antonym term. I don't know of any other uses but the meaning seems clearly orthogonal to whether the students were athletes or getting special treatment for some other reason.
Are there tools that would provide occurrence counts like Google n gram for the last couple of years that would be able to provide meaningful results for nearby uses of other two-word terms? Perhaps a statistically relevant sample could be made of the texts where 'paper classes' and 'real classes' occurred near each other to determine how often they bore the antithetical meanings above. Then some other work could fine other word pairs '* classes' appearing more frequently than 'real classes' near 'paper classes', and they could be similarly analyzed for relevance. that would provide solid empirical evidence to answer your question, but might be too much work.