The relationship between education and earnings is not entirely market driven. Within the government sector, pay grade is affected by education levels. Government also has educational credentials that affect many professions, including teaching, health care, and law. That is why I do not look to signaling as the explanation for the returns to schooling. For signals of ability, there are alternatives available. But strict credential requirements leave no alternative.
There is more at the link. While I trust the best individual researchers in the area, I share Arnold’s fear that the macro-organization of the education field is not structured to produce totally objective results. Still, a natural experiment showing a high signaling premium would yield accolades to its author and I still would like to see your nominations for the best work — and I do mean natural experiments — pointing in this direction.