Amanda, Once we'd laid down the ground rules, which I did in the school not the stable, I started off with in-hand work, then onto under saddle - it's fab for this. My reasons for doing it this way round was that it it was then fixed in horse and human heads as a training discipline and there was no misunderstanding about when the treats would appear (does that make sense?) If you've laid down the ground rules OK then you will find you can transfer it easily enough - just go back a few steps in the new environment first.
I have some expressions too carried over from pre-clicker training which now mean 'good try, you're on the right track'. It's fascinating what the horse understands - for example 'good girl' in-hand or on long reins is still a 'bridge' but was picked up by J as equivalent to a click under saddle! (I need to use 'clever girl' under saddle........golly it keeps you on the ball this training stuff

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I know what you mean about the pratty moments, my Sec D goes off into 'welshworld' every now and then.
Just like any training you have to break things down into little chunks ie, can you do a quarter circle withoutbeing pratty, now can you do a half circle etc. Pace would be another lesson, the other way round another, quality of pace another etc etc..... It has made a huge difference to me (I'm just a rank amateur) but never make the mistake of NOT putting your whole heart,soul and attention to it, the horses always know and won't concentrate/communicate either, personally I think that's when mugging and other problems can start.