I instructed at a flight school that did accelerated training. The result rarely had much to do with the pace of the training program. Just as with the traditional way of doing things you have good and bad students, those that study and show effort and those that don't. The students that came prepared and gave 100 percent while training usually had no problems. I would rather work with someone everyday to get things done than once a week. Anyways, Some people are just not good at flying and may never be, no matter how much time you give them.