Instructions
Start teaching your horse this movement when he can move over from pressure of your leg, bends easily through circles and accepts the rain contact.
Ensure that you are in sitting trot rather than posting and that the horse has a free moving pace in a steady and even rhythm.
Use a corner to prepare for the movement, which will help the horse establish bend. As you leave the corner, guide its' forehand off the track by opening up the inside rein.
Check that your shoulders are at the same angle as your horse's shoulders by bringing your inside shoulder slightly back.
Keep the inside leg on the inside of the horse near the girth to make sure he keeps bending and does not bring his hind quarters off the track. Use your outside hand to steady the pace with a gentle squeeze. Keep the outside leg steady just behind the girth.
Check that your inside rein is as soft as you can make it without dropping the contact. Resist the urge to pull your horse's head off the track with your hands.
Look diagonally across the arena through your horse's ears and keep using your inside leg to maintain the movement. If the horse understands what is required, keep your aids and signals as still as possible so that you do not inadvertently interfere and cause him to lose the movement.
Finish the movement by straightening the horse up before the corner and make sure that you award lavish praise.
How to Teach the Shoulder-In to a Horse
Shoulder-in is one of the most important strengthening and suppling exercises for horses and is used extensively in dressage training. During the movement, the horse's footfalls are on three tracks instead of two tracks. The outside hind leg --- the one nearest the boards of the arena --- travels on the first track, followed by the inside hind and outside fore on the second track and the inside fore on the third track. The horse is bent inwards and its' inside hind leg does most of the work pushing the horse forward.