I would agree with acelockco when he says:
The dive training agencies are lacking and again are concerned about getting training classes and of course profits from them. They want as many certified divers as they can get out there so they can sell more classes and more gear.
If they would focus on really lengthy and in-depth training, forget trying to make everyone pass. I always see people in SCUBA class that I honestly feel should not be diving because they just don't feel comfortable and can't ever perform things right without help. Those people will usually panic in an emergency. BUT we have to teach them and get them certified, because the agencies tell us so. They will always get certified even if they have to take the entire class again, unless they quit. So even if they don't belong in the water, eventually they will be certified if they really want it.
They say PADI stands for Push Another Diver In! Although it isn't just them who try to certify everyone regardless of ability. A couple of years ago I did an SSI course - Nitrox whilst on holiday in the Maldives. We were given 1 day to learn the information - I expressed concern to the instructor that I didn't really understand all the complicated formulas etc. I was told 'don't worry you will be fine'. I took the test and he then said 'you need 1 more mark to pass - try some of the questions again.' I told him I couldn't because I didn't understand it. To which he replied 'well just guess you never know you may be right (it was the normal multi-choice). I told hime I wouldn't and I would rather fail as I didn't want to pass when I didn't understand it - I would hardly be a safe diver through guessing! He then sat and explained the formula to me properly using another example, leaving me to complete the test one. This I was able to do. I can only assume he hadn't the time or inclination to spend time with me in the first place. I haven't used Nitrox to this day because in all honesty I don't feel qualifed/confident and I think this is down to rushed training and not enough support!!!!!