Ground driving — working the yearling from behind with two long lines attached to a surcingle or through rings on the halter, simulating the rein contact a rider will eventually apply — is one of the most valuable pre-riding preparations available because it introduces the concepts of bit contact, steering, and stopping from a safe position behind the horse before any weight is ever placed on its back.
Ground driving is introduced in stages. The first stage is teaching the yearling to accept lines running along both sides of its body and around its hindquarters without panic — the sensation of a line touching the hind legs is alarming to many horses and must be desensitized before any driving work can proceed. This is done on the ground at rest, running the long lines gently along the horse's sides and around the hind legs until the horse stands quietly with both lines in contact.
Once the horse accepts the lines, the handler positions behind and to the side — not directly behind, which is a kick risk — and asks the horse to walk forward. Initial steering is minimal; the priority is simply establishing forward motion in response to driving cues and stopping in response to gentle backward pressure on both lines. Direction changes are introduced once forward and stop are reliable.
For western-oriented yearlings, a snaffle bit is sometimes introduced during ground driving in the yearling year — the horse learns to accept the bit in its mouth and to respond to simple rein pressure before the additional complexity of a rider's weight is added at the two-year-old start. For English horses, ground driving with bit contact is a standard part of preparation for backing and is particularly emphasized in classical dressage training traditions.