It may not have anything to do with what you've retained. Mayhap you've retained everything you should have done.

True enough everyone is different, but learning patterns are pretty much established for the majority. And I am talking about what will be retained regarding physics, etc, not just how to clear your mask. My concern is how much a student retains of what they were taught, assuming they were taught all of the required materials and did the book study as they were supposed to do.

I'm certainly not arguing a "hands on" approach as you call it. This happens in the pool sessions and the open water portions of a properly instructed course, regardless.

A fish and a bird can fall in love, but where will they build their nest?