Teaching a horse to yield laterally from rein pressure — to move its body sideways in response to a rein cue — is one of the most important applications of the yielding principle because it underlies every lateral movement in both Western and English riding, from a simple turn to a half-pass or spin. The foundation of all lateral rein responses is the horse's understanding that pressure from the rein on one side means move the body away from that pressure in the indicated direction.
The teaching sequence for lateral yielding from rein pressure typically begins on the ground with direct lateral rein pressure from the halter — applying rein-like pressure on one side of the halter and asking the horse to step its hindquarters or shoulders away from that pressure, depending on which exercise is being developed. The ground work establishes the concept of moving away from lateral rein contact before the complication of a rider's weight is added.
From the saddle, lateral rein pressure is introduced gradually and always with clear intent — the rein applied with a specific direction of desired movement in mind and released the instant any yielding toward that direction occurs. The horse may initially respond to lateral rein pressure by turning only its head rather than moving its body, which is a partial response rather than a full lateral yield. The handler progressively refines the exercise by asking for more body movement and less head-only turn over many sessions.
The quality of lateral rein yielding is one of the most reliable indicators of the depth of a horse's overall yielding education. A horse that yields its whole body softly and responsively to light lateral rein pressure — moving its shoulder, its rib cage, and its hindquarters together in the indicated direction — has a level of suppleness and responsiveness that reflects years of quality pressure-and-release training.