I have been reading all the answers and agree with both sides, you have to work out what method you use, you have to get inside your horses head, he is young and there is no wrong in taking him back a few steps,my horse was four when we got him, fine hacking out in company when when we started to take him in the school he would nap at the gate and if asked to move would rear and buck, I had all the usual comments of broom up his behind and lunge whip round his hocks, thank goodness I didn't, I later found out he had had a rough time in the school. I took him back a few steps, done join up every day and I dont mean for a week for at least a month and trained him to go from the voice, walk, trot later on canter , all the downward transisition, stand, turn for change of rein, I then repeated this with tack on, if he napped I drove him on with the lunge whip, never touch him with it, then my daughter was put on board, still going from my voice, she just sat there, she then gradually took over with her voice and I gradually took my voice away. You wont achieve this overnight, you need patience. Please dont think I am airy fairy with my horses I am not and insist on good manners, on and off the ground, but with a horse that has had bad experience in the school and at such a young age you have to be very careful, otherwise you'll end up with a very angry horse. When it came to hacking out, I reverted back to my voice, if I said walk on 100 times I didn't care, I had a friend follow me in a car if I got into trouble, I never did, cause all the work had been done in the safety of the school, I became his leader so he depended on me for his safety, what I said went, his confidence giver. I hope this helps but dont expect overnight success.