"When Mary went to get back down onto the mounting block her foot slipped, and both the mounting block and Mary ended up underneath Apple! Apple freaked, took off, and trampled Mary on his way! Now both horse and rider are petrified and Mary hasn't been able to get back on - what on earth are we going to do?!"
What we did was break the end goal down into small, achievable steps. Firstly, we taught Apple to move forwards, backwards, sideways, and around, when asked. Next we asked him to stand by the mounting block, with no one on the block. When he did this for a few seconds, I led him away - remember it's the release that teaches the horse that he's done the right thing.
We progressed to having someone standing on the mounting block, and asking him to stand. Initially he chose to stand on the wrong side of the block - that's fine, it's still standing. Gradually we asked him to stand the other side of the block, and then another. I kept rewarding him by leading him away from the block when he got it right for a few seconds, but only stroked and talked to him when he was standing by the block. The release of leading him away lets him know he's done the right thing, but the stroking and gentle murmuring when he's by the block lets him know that it is a safe and comfortable place to be.
Finally, we employed the 'moving over' work. I used a schooling stick as an extension of my arm (because I don't have Go-Go-Gadget arms!) to touch the far side of his quarters and ask him to move them towards me, whilst I was standing on the mounting block. Initially he found this difficult to understand, but as always, the key is in releasing the very instant he responds, this has to be instant, so imagine the release has to be as quick as if you had touched a burning hot oven.
Because Mary was so nervous, I did the majority of the initial work myself. This meant that Apple could learn more quickly, because my experience made my timing and application more accurate than Mary's would have been. I talked Mary through the whole process, and once Apple understood, then Mary was easily able to replicate it.
Within 30 minutes, Mary had got on and off Apple at least 20 times, and I set her homework for the next few days of mounting at least 50 times each day. A couple of days later I had a report back "Apple has been really good to get on. He's presenting himself to the block and moving away from the stick if he's too far away and I need for him to straighten up. He hasn't moved a foot on any of the numerous times I've got on him. I feel so much more confident now - thank you!"