:lol: You did ask the question how to I teach my horse to jump a 6 feet jump :lol: While may be it seems straight forward and takes only a second, as a jumper you know that it’ll take time and talent to jump it.
but it could be an interesting conversation how people started their horses on half steps?
Piaffe and passage are taught by first getting a “half steps” and yes, you can start to teach your horse half steps as early as at age 4. With such young horses you “boil milk” and let go as soon as you feel milk is overflowing. Be careful, if you don’t have experience, you might get hurt by a young horse while “boiling milk”. While piaffe and passage has quite strict rules, half steps are generally something that resembles either one. Getting from half steps to real piaffe and passage is a huge deal in itself. Getting from half steps in turn out to half steps in arena is a huge deal. Getting from half steps that are taught on the ground to half steps that can be done under the saddle on a queue is another huge deal. I’ll repeat that please be very careful, it’s easy to get hurt teaching half steps.
Another way is to complete the prerequisite work:
*Clear transitions: down and up transitions should be very clear and on the bit and lowering the hunches in those transitions.
*Clear transitions with in the gait: extended trot to collected trot and work on the 2-3 steps of those transitions, since this is where the half steps live.
*Obedient canter/walk transitions in self carriage focusing on loading of the hunches = to develop hind end muscles + abs.
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Marching walk pirouettes with marching hind legs on the spot = to explain the idea of marching on the spot.
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Loaded, correct Rein Back with correct loading of the hunches = to explain the correct loading of the hunches.
If you have those prerequisites, you can start on the actual exercise of teaching half steps. Start on collective walk on the long side and at E do a walk pirouette with the hind legs clear picking up and down in the even rhythm almost on the spot = on the last step of the walk pirouette ask for the very collected trot and think “rein Back” to boil milk for 10 steps. After 10 steps ask for the Halt/Rein Back then trot out of it in very collected trot and keep boiling milk. How to boil milk? With gentle touch, minimum aids and feeling! That’s how I was taught.
Some horses can get half steps in weeks from that. Others will take years. The real difficulty if teaching half steps is a danger of being hurt if you don’t know how to teach half steps. When milk over-boils it’s almost impossible to fix it and horse starts to be more and more dangerous with every over-boiling of milk.
PS: you say “very accomplished Prix St. George rider and trainer” = remeber there are many PSG riders and trainers who have no clue how to teach half steps 
