Externships for Students or Employment for Graduates?

An empirical questions keeps occurring to me and it deals with the relationship between externships and employment. By externships, I mean the practice of law schools to grant credit to students who work for government agencies and various corporations without compensation. If schools offering these opportunities are true to their promises, these students are are not just fetching coffee and typing. Instead, they are often doing what a law school graduate might be doing if someone were not already doing it for nothing. Of course, externs take the jobs of others even  if they are only typing and fetching coffee but law schools aren't inclined to worry the "little" people. While encouraging externs, law schools wring their hands about the employment opportunities of graduates.  Part of the wringing can be traced to the negative impact that low employment rates  have on national rankings but there is also generalized worry about the future of the institutions, positions, and income.

Of course correlation does not mean causation. There is clearly a correlation between externships (free labor) and the unwillingness of employers to hire graduates (paid labor). It would be silly, though, to think more externships have caused the current conditions in the market for graduates.

But wait.  Is there really no impact at all? Is it really possible that hundreds of students willing to work for nothing actually have no impact on those who would like to be paid? I doubt that. That leads to question about just how much of an impact there is. For example, do 20 externs lead to one less full time paying job?  Externs and graduates are in many respects perfect substitutes, One is priced at zero. The other is not. If you were a profit maximizer, which would you choose?

So, are law schools offering an opportunity to current students that is paid, in part, by recent graduates. I think so but I cannot say  how much.