Seconded on the Howard Kobata dvds. He just released his second set which better describes the drills he uses. It may seem a bit controversial because it's not exactly the way we were all taught (at least I wasn't), but he explained it enough for me to open my mind and make sense of it. I love that he helps teach us how to teach it to the kids and look for common mistakes. It's one thing to know the information, another to know how to convey it.