Greg Mankiw writes about human capital, and the implication from his post is that human capital is synonymous with formal education.
This is a completely false understanding of human capital.
For the purpose of this post, I define human capital as that mysterious something which allows one person to make $200,000/year or even $1 million/year, while other less fortunate people are earning the minimum wage.
It should be obvious that education is only a tiny part of what constitutes human capital, because immediately after a person graduates from college he is able to earn only a slight bit more than he was before he had a college degree. There are many college grads waiting tables, working at Starbucks, etc. The market puts no value at all on their college degree, indicating that the college education is not what’s creating the human capital.
It is the work experience which allows people to earn more money, so this means that people accumulate human capital by working at jobs.
One may even go so far as to say that a college degree, instead of imparting human capital, actually acts as a barrier to entry limiting the number of people who can board career tracks where they obtain the genuine human capital.