I am very old school, and stopped teaching professionally in 1989. Afterwards I and my wife did only train our two sons.
Our idea is that the training for scuba requires necessarily to master, one after the other, the following steps:
- swimming at the surface: at least 100m in less than one minute, both frog and crawl. Floating vertically with a weight of 5kg using alternate frog kicking and one-hand opposition for at least 3 minutes.
- swimming underwater (frog style, at least 25 meters horizontally, at least 5m vertically)
- snorkeling with good surface kicking with proper fins (at least 400m in less than 4 minutes)
- free diving with fins and mask (at least 50m horizontally in the pool, at least 15 meters depth in the sea)
- learning the "capovolta" (upside-down manouvre) for submerging when positively buoyant
- scuba diving with basic equipment (no BCD): breathing control (with the famous and generally deprecated inspiratory pause), mask removal and breathing without it, mask evacuation, buddy-breathing with a single reg, horizontal swimming with different kicking methods, vertical swimming with powerful free-diving kicking style, submerging with the "capovolta" when positively buoyant, counter-effecting strongly negative or strongly positive buoyancy using breathing control, fins and the the "hands opposition" technique.
- scuba diving with complete equipment: wet suit (forbidden in all previous steps), BCD, torch, computer, camera, etc.. Each piece of equipment is added one by one (the suit is the first). The BCD is very important and requires a lot of time for mastering buoyancy, trim and safe ascent procedures.
- nautical training about boats, knots, winds, waves, ladders, anchors, lines, sea-sickness, and all that is required when sharing a small inflatable boat with many other divers.
As you see, in this old-style approach the BCD is one of the very last things. But this is how I always trained my students, with very good results. I do not know if this is still feasible nowadays, as it requires at least three months in the pool and at least 10 sessions in the sea, the first half without scuba equipment.