The discussion of training shortcomings in this thread seems focused on agencies not wanting to flunk students. I don't think I should have been flunked; I think they should have taught me more.
My OW course did a **** job of teaching bouyancy control. The PADI manual emphasizes taking slow, deep breaths. Italics in the original--I just checked. Nowhere does it say that breathing as deep as you can will have you bouncing all over the place; I had to relearn to just breathe normally from one of my AOW instructors (and still not the book.) Nor did my OW course teach me to exhale fully while deflating my BCD to get under initially. Fortunately, unlike (apparently) many OW courses, they didn't overweight me, so it was a little tricky to get down; no one offered me any tips on that (there were about 5-6 instructors and assistants in all, 3 at a time during the first 3 ocean dives) until the last guy on the last day advised me to use my arms to push myself down.
Dive planning was even more neglected. The manual gives an example in which you and your buddy agree that 50 bar/500 psi is ample reserve pressure, and "based on the depth" (not specified, though presumably 60 feet or less?) "you agree that you want to save 20 bar/300 psi for [your ascent and safety stop.]" Then it walks you through the math of figuring out your turn pressure, but never says anything more about where those figures came from. It then gives you an exercise in which, "due to conditions" (what conditions? Current? Low viz? Surf? Drunk captain? A sociopath in the White House having access to the nuclear codes? All of the above?) "...we are planning very conservatively," which in this case means 800 psi reserve and 500 for ascent. Which figures should we use and when? The book is silent. My instructors didn't cover this at all in class; when I asked they gave vague answers. On the final checkout dive, we were to plan the dive with our buddies and then share the plan with the group. I was in a trio and suggested we use the 500/300 numbers from the first sample, since we'd just assessed conditions and, as confirmed by our instructor, they were "ideal." One of my buddies brought up the rule of thirds, which wasn't mentioned in the course but he'd heard about somehow. My other buddy suggested taking the average of my number and the other guy's, so we did. Our instructor said it wasn't conservative enough but didn't explain why. The next buddy pair exchanged glances and offered a more conservative number. The instructor said that was fine, but that we wouldn't be turning the dive at the turn pressure we'd picked; we'd turn it when he said to. I felt like this was defeating the purpose, but at this point I was so tired of being that student that I didn't bother; just took my cert and vowed to get more and better instruction somewhere else before I dived alone.
Also, the predive checklist--BWRAF--says to test breathe your regulator two or three breaths. Then, in a separate sentence, it says to check your air pressure gauge to be sure it shows a full cylinder. Nowhere does it say or imply, nor did my instructors mention, that you should be watching the gauge while you take those breaths to be sure the needle doesn't drop suddenly, which could indicate your air was turned off after having been turned on. I learned that, not from OW, not from AOW, but from reading Diver Down, the Red Asphalt of scuba diving. And I used that knowledge just this past weekend, when a "helpful" boat captain mistakenly turned off my air--but I caught it before splashing in.
I've learned so much from the independent reading I've done and the pros I've had a chance to interrogate, stuff I feel I should've gotten from my OW course. I executed all but one of the skills correctly on the first try; the remaining one, underwater compass navigation, wasn't itself the issue so much as I lost control of my bouyancy and had to do it over. The instructors I've had since OW have all told me my bouyancy control was better than most people they've seen with my level of experience, and I gather from the groups I've dived with that my air consumption is about average for where I am, and it's getting better. I missed maybe 2 questions in all of the tests and quizzes in the entire course. I'm capable. I just needed to be given more.