The ordinary pet dog trots to heel, but the future guide dog must be encouraged to lead the way and walk on the left because the blind owner holds the harness with the left hand. It is encouraged to walk with the head held up looking out for obstacles and potential threats. read more
Now, a person who lacks a left hand, or lacks the ability to use their left hand to hold the harness, can be trained with a dog that has also been trained, to guide from the right. The body movements, hand signals and commands differe slightly to accommodate the changeover. read more
People tended to keep left when walking too, so keeping a dog to your left kept them further from other dogs and people, and if walking alongside a road or on a shared path, it kept them away from traffic. read more
Dogs are trained to walk on the left simply because for right handed people it's easier to make turns and not trip over your dog. I have dogs that for draft work are trained to work in front, behind, on the left and on the right. read more