...was suggested by Australian Andrew Rand. It pretty much sums up everything.
Most entry-level students CAN master fundamental buoyancy skills..., even in today's more condensed time frames. But they can't do it if YOU keep teaching the same way we did in the 70s and 80s.
Balanced equipment. Proper weighting. Breath control. That -- and your constant admonishment to "stay off the bottom" and "stay horizontal" -- is all it takes.