I don’t know many horse people who wouldn’t get a kick out of whistling or calling their horse’s name and having him come running across the pasture or arena. On top of it being a practical thing for your horse to know, it gives you a great feeling.
When a person wants to teach a horse to come to them, it’s quite common practice to turn the horse loose in a round pen and do ‘join-up’ or a similar form of round pen training. I have nothing against round penning a horse, and I do it myself, but if a horse is already halter broke and gentle to work with, I usually find that I can teach him to come to me much faster and easier if I start with a halter and lead rope already on him. I like to teach the horse to come to me while I have a physical connection to him and then later on, when I turn him loose, he already has a pretty good idea of what I want him to do when I call him to me.
The only tool you will need besides the halter and lead is a lunge whip. It is only used to motion toward the horse and to tap him lightly at times. At no point should you be aggressive with the whip.
Start in an arena or round pen with your horse standing with his right side beside the wall of the round pen. Stand facing your horse so that your left side is beside the wall. Hold the lead rope in your left hand and the lunge whip in your right hand. Also hold the lash of the whip in your right hand so it’s not swinging around.
Now, pick a word that you are going to use to call your horse to you. Aside from his name, a word such as ‘come’ or ‘here’ works well. You can also whistle, as long as you are able to whistle loudly, because your horse will need to be able to hear you when you’re eventually calling him from greater distances.
To begin the exercise, tap your horse lightly on his shoulder with the lunge whip, say the word ‘here’ (or whatever word you’ve chosen) and walk backward. If your horse doesn’t follow you, don’t worry about it – as you back up the lead rope will tighten and that will pull him to you if he doesn’t come on his own. Go a short distance and then stop. He should stop and then you can reward him. It’s good practice to scratch him on the withers with the end of the lunge whip so that he learns the whip is nothing to be afraid of. Repeat this exercise a lot. Once your horse has it figured out, forget the tapping and just motion toward his shoulder with the whip as you call him and back away. Calling him is to be his cue, but you backing up is important because when you back up, it creates a space for the horse to fill.
The next step is to repeat this exercise on the other side. Stand your horse with his left side beside the wall while you stand in front of him, facing him with the lead rope in your right hand and the whip in your left.
Once you have worked on both sides along the wall, the next step is to lunge your horse around you on a small circle. Circle him to the left around you while holding the lead rope in your left hand and the whip in your right hand. Now, call him to you and back up. As you do, swing the whip under the lead rope and over to your left side. This will cut the horse off, and as you back up, help guide him to you. The whip doesn’t touch the horse at any point. Back up and bring him to you and reward him when he’s up to you. Repeat this exercise many times, gradually making the circle that you’re lunging your horse on bigger and bigger so that you’re calling him in from greater distances. Do this at the walk and trot. Repeat this exercise in the opposite direction. If you’re having trouble at any point go back to working your horse on smaller circles.
The next step is to turn your horse loose in the round pen. Move him around the pen at a trot. When he turns his head and looks at you (even a little bit) call him to you at that exact moment and back up. You can move your whip a little bit to help cut him off, but be careful not to move it fast and scare him. If the work on the lunge as been done properly, he should come right up to you. Reward him if he does. Repeat this exercise both ways.
Eventually, you will just have to catch your horse’s attention, call him to you, take one or two steps backward, and your horse should come to you. This may take several weeks in some cases so don’t be in a hurry.