The lost secret can be found with an understanding of philosophies of education.
There are many, including 'experimentalism,' of which so-called 'Progressive Education' is but one species.
Progressive Education, propounded by John Dewey a century ago, dominates the education departments of every teaching institution in the United States. You are not looking for a teaching degree, but if you were, you would have to buy this one variety of one philosophy of education to get a teaching degree.
It didn't happen overnight, but that's the demon that lies at the heart of our sorry education system.
It allows for no alternative, at it is even alien to the tenses at the heart of the English language.
If we began today, it would take thirty years to displace.