I see many people struggle with the side pass. Often their horses have not had enough basic work leading up to the side pass and sometimes the horse is just not ready. This makes for lots and lots of resistance on the part of the horse.
So briefly, here are some of the steps I go through in developing a good side pass: First, the horse must do good walking and small jogging circles - bending through them with their whole body, stepping up with their inside hind leg and dropping down nicely into bridle while wrapping around my inside leg.
Second, I like to spiral the jogging circles, making them large then small again by applying my inside and outside leg appropriately. This begins to move the horse's rib cage. The rib cage is so important!
Next, I like to teach a counter bend, preferably at both the walk and jog. Often it is easier to introduce this maneuver from a jog as the momentum really helps. Again, make sure the horse is yielding softly and dropping down in the bridle.
I rarely find it necessary to use a fence when teaching a side pass, it's just not necessary and I think it can create another set of problems to deal with later. I also rarely start a horse side-passing over a pole, I'll introduce the pole later, when the horse is comfortable with the basics of the maneuver.
When the horse is totally comfortable and accepting of all this, then I start the side pass. I like to ask my horse to step forward (from a stop, then ask him to move laterally over. Be sure to give your horse a space to move into by releasing or opening up your leg on the side the horse is moving into. If the horse starts to lead with his shoulder, I stop the shoulder (essentially blocking the horse momentarily with rein and my leg slightly in back of the cinch) and move the hip until it is in line with the shoulder. If the horse's hip is getting ahead of his shoulder, I open my off rein up and "push" the shoulder with the opposite rein and use my leg right at the cinch. If the horse gets balky and resistant, I move him forward and try it again. If he's still resisting, I might work on something else for a while, let my horse clear his mind, then come back to try the side pass again with a fresh start.
I always finish a side pass with the horse's body in a straight line - never curved. Over time you will get a nice side pass with the horse crossing over in the front and the back. Hope this helps! Talk to you next week, JD.