When he finally controls himself all of the way without pulling forward even one bit, you allow the helper to give him a several goodies. Please note that there are no corrections in this game. The dog must learn to choose for himself to maintain a proper heel position with a slack leash. For this choice, he is rewarded. If he makes the wrong choice to try to steal the food, he has to wait that much longer to claim his prize.
Dogs hate that part.
It's worse than yelling or giving stern leash corrections. The beauty of it is that instead of relying on the owner to yell and give leash corrections, the dog learns to control himself . This is an excellent exercise even for rank beginners. I use it in my basic obedience courses, and the people are amazed at how fast the dog learns to correct himself and stay in the loose leash heel position without any harsh corrections. It is good for your dog to know that you control the rewards, even when you don't have the food.