Ok, going to add my two cents worth.
For a dog to pull they have to have something to pull against. To teach a dog not to pull as a handler you have to become ultra aware of the leash and how much pressure or how loose it is. People become so use to *holding* their dogs, that they don't realize just how often or how much they are pulling (the handler pulling and/or holding, NOT the dog). The end result is a dog and handler that are *dull* to the leash and dogs that pull.
When you are training, if you can have someone watch or video (they don't have to a dog person nor a trainer, all you need are their eyes), you maybe very surprised at how often you take up the slack etc.
Personally I find it easier to train a dog loose leash walking while*going someplace* instead of around in circles etc. Most dogs are motivated by going for the walk .......dog park.........car (whatever).
Start out with the leash loose, BUT not holding it at the end, that allows the dog to get to far out front and it also allows them leverage. Start with them standing quietly and calmly on the loose leash beside you, click and reward, if at ANYTIME the dog starts without you, just nicely and gentley bring them back to the correct position BUT don't give them a reward, because if you do, then you are rewarding them for leaving in the first place. The walk doesn't start until they are how and where you want them. THEN start to walk, (remember don't give them too much leash, but enough to allow slack when they are in the correct position), if the dog starts to forge ahead or pull, STOP, nicely bring them back to position (standing is fine), loose leash, start forward again, IF the dog gives you a loose leash, click and reward!! The first couple of walks (I find they figure it out during the first hundred feet if you are doing it correctly) can be difficult and long. You have to have patience and TIME, so don't do this if you only have time for a quick walk. You have to have the mind set that you have all the time in the world to get to where you are going. It works the same for a dog that bears out to the side as well, bring them back to position, go to a loose leash and start forward again. Always click and reward in the beginning for a loose leash, and always stop forward motion when the dog even starts to pick up that slack to the front or to the side. But you have to become aware of the leash, if you stop to talk to the neighbor, make sure you DON'T have an ounce of pressure on that leash. Normally for dogs that pull, their owners get into the habit of ALWAYS holding them with a tight leash, therefore it is often a learned behaviour.
Good luck
Lynn
