We find that employer learning about productivity occurs fairly quickly after labor market entry, implying that the signaling effects of schooling are small.
Here is much more. And here is more yet; this second paper estimates the speed of employer learning and uses that estimate to bound the value of the signal at no more than 28 percent of the value of education. I consider this devastating to the signaling hypothesis. How can ?? years of schooling be needed to signal your quality, if your employer often knows your quality within months?
In my view education is mainly about indoctrination to give you more productive habits. So yes it is learning, but not in the way they might have told you, and that is why it so often does not feel like learning.