Alfredo had her start on a 20 m circle at the walk, then had her pick up a counter-canter. After about half a circle, he had her walk, then pick up a true canter for another half a circle. Then walk, counter-canter, walk, true canter.
After perhaps half a dozen repetitions of this, he added a haunches in/haunches out element. So, walk with haunches out, transition to counter-canter. Counter-canter with haunches out. Walk, haunches in, transition to true canter with haunches in. Walk, haunches out, counter-canter...
As she was able to ride the exercise better, he started asking for more precision with the haunches in and out. Walk with haunches out, transition to counter-canter keeping the haunches out through the transition and during the counter-canter. Transition to walk and IMMEDIATELY haunches in at the walk, transition to true canter with haunches in through the transition and the canter. Etc. Again, these movement were repeated again and again.
Eventually the movements were coming very, very quickly, with the horse easily moving his haunches in and out. And then, during one counter-canter-haunches-out, instead of asking for a walk transition, Alfredo yelled "Haunches IN!". And the rider switched her aids for a haunches in, and the horse did a perfect change right on the aids.
I think part of what worked here is that she didn't quite know what was coming, so there was no anticipation on either the part of the horse or the rider. Plus, the horse was so in tune with moving his haunches over that the change was easier than the transition. And of course, he was changing from counter-canter to true canter, so that was easier too.
They did several more changes, and although the horse got a bit leapy in the changes, he DID them, every time. The set up was great and you could see he had no problem with it. The rider was smiling ear to ear too (in between gasping for air... she was working HARD and I was really glad it wasn't me!).
So... do you have any secrets for teaching changes?
No media of other rider, but here's another pic of Taran from the clinic.