The way I taught mine was to walk her to a fence where she can't walk forward. I gave her the cue of "side". I used my legs to put pressure on her to get her to move away from me. I'd work with her for 5-10 minutes every day until she got the idea of what I wanted. After she got comfortable with that, I moved her to a place away from the fence and worked her there. Once she got that down, I moved in front of her to give her her cues. I use a riding crop to extend my arm if needed. I don't smack her, just put pressure on her hip to keep her hips moving with her front. You can teach them word cues too. You can use gee for right and haw for left (same as driving cues)
We went through this with our 2 yr old filly & we did teach her
Get a 2x4 about 6 ft. long. Walk your horse over it so the 2x4 is under its belly.
Stand at your horses side, pull the head towards you, use your finger & push the
hind quarters away from you. Do that back & forth untill you clear the board. Use your knee against the horse's side if you need to.
Use a word for the deed. We use the word PASS.
This can take a while, depending on the horse. Always praise the horse & just when you think they will never get it , you will line up to practice & they will pass down the line without you touching them.
When you have mastered the deed be sure to teach them to pass the other way too.
Another way I was taught is to use a whip--hold the small end in your hand or a piece of PCV pipe works well.
Put their butt to a fence, stand in front--hold under the halter with left hand and tap the pipe along the right side of horse and say side. Move your body left , as you cross over your feet and move left they will move with you once they get the idea. One or two steps at a time and praise them. The pole makes them understand to move both front and back together. Say whoa when you stop and drop the pipe down so they will also stop when you need to
You know I tried this with Rabbit the other day ( don't worry, at 26 there is NO way I am going to start Obstacle with him, I was just fooling around
) I just had a halter on him and we were standing his round pen. I thought about it because I haver seen lots of people ask about it, and it is something I have never done. So....how to start with an old horse who is NOT about to learn anything new?? Use a command he has always known. Logical?? I asked him for "over". When he started I engaged his front end. He was a little surprised but I've this to him all his life so he just moved his whole body over instead of his rear. He did three steps of perfect side pass before he started to swing round. Time for praise, and now I'm hooked. It took me five minutes to have him side passing across the ring, in sets of four (ie four steps, half halt- praise, four steps, half halt, praise) not perfect but he's an old horse and he finds this hard so I'm not about to push it. So, my advice?? Start with a command the horse already knows and understands. You will never get a good side pass until the horse is touch sensitive- ie moves away from your hand, instead of pushing against it as he would do instinctively- so, if the horse does not "get over" to command, that's the first thing to teach him. I taught my mare Amira shoulder in and full pass in an afternoon, starting the same way, but this was from the saddle, and I found it easier. I see no reason why, however, the same principles cannot be applied to ground work- make it easy for the horse to learn, and the horse will learn more easily
I use the word "side" for side pass. Many times my horses will learn to sidepass right away and sometimes I need to break it down into haunch and forehand turns and then combine those movements. I don't use a pole to start as they can worry about the pole and have divided attention. I stop forward movement with the leadrope and cue saying side and clucking. I stand about girth area and increase the volume and speed of my cues rather than touching the horse. If I get one sidepass step I praise (good boy/girl) and pet and ask again. Minis are smart and it doesn't take long before they can give me several steps.
For the horse that doesn't get it and starts getting frustrated I break it down to simple forehand turns saying "over". This is probably the easiest to teach and when the horse gets that then I move on to haunch turns stopping the forward movement with the leadrope and touching the shoulder to get them moving away and giving them support to keep the body straight. Remember that haunch turns are a forward movement and allow them the room to move forward to cross over rather than rock them back on their hind legs. You only want to start with a few cross overs and not more than 1/4 turn before praising and stopping. By trying to get them to do a 360 the first time will result in falling out and incorrect turns. Better to have a few correct movements rather than fighting and teaching incorrect movements.
Once they can do both movements they will understand stopping forward motion and moving away from you. Go back to first paragraph and try again. Don't forget the praise and petting stage as this is a very important tool for future use. They know what it means and I can settle my horses in the arena during a class by saying good boy/girl if they start getting a little strong.