In my basic course, I do not discuss or even introduce the haul. It is an advanced technique in any of its forms. To become a "complete" fly fisher, I believe the student should master a smooth stroke before entering the "hauling arena." I've had several students in advanced casting who learned a form of hauling either on their own or in some other school; unfortunately, the hauls they practiced merely served to cover-up errors in their basic mechanics. It took much longer to correct long-standing errors than it would have to teach them the haul when they were ready.
The two errors I routinely see, and the most damaging to successful fly casting, include: (1) allowing slack to form before beginning the backcast and (2) not watching the backcast ... Both are killers! I've gotten mean in my old age. As a student you get to form slack twice without penality; after that, you privilege of laying the rod on the ground, walking the thirty or so feet to the fake fly, and then pulling out the line until it forms a straight line with the rod's tip. You then retrace your steps to the casting position and pickup the rod. If you raise the tip more than a few inches from the ground, slack will again form ... so, you get to repeat the process all over again. I've found this to be a very good technique that will change a bad habit.
For those who do not watch their backcast, I stop their stroke and have them try to describe what their line did. This can become very embarrassing, especially when others are watching. In the end, these folks begin to watch their backcast and come to understand the transition from the back to the forward cast. More importantly, they learn to lay out a backcast in a straight line.
When I was a bit heathier than I am today, I practiced 5 to 7 days a week and averaged about thirty minutes per session. After my back surgery, I'm down to about three times a week with a shorter fifteen minute session. Practice makes perfect. As I've said before, the fly cast is like the grooved swing in golf -- somtimes it's on and sometimes it's not. When it's not, time to return to the practice tee.