In my opinion, ground driving or long lining is an absolutely crucial part of training. I am a HUGE fan of it. I think you should do a ton of if before you get back on. It worries me a bit that you are already up on the horse and needing this lateral flexion "to teach him how to steer". Steering imo needs to be taught before a rider steps up, otherwise it's just kind of like getting in a car with no steering wheel. It might be alright for a while, but best case scenario you're just a passenger at the mercy of the car/horse/whatever, hoping for the best if something happens.
It sounds like there's something bigger going on. Either he's in pain or uncomfortable or things are moving a bit fast for him, or maybe the signals aren't coming through 100% clear to him, which may be why it's not translating over to the under saddle work. Hard to guess over the internet though.
From the limited information here, if it were me I would definitely do a ton of ground driving, get him good and solid with everything there first. Steering, backing, whoa, drive him all over the darn place. In the round pen/arena, around the farm, over obstacles, trails, around scary things, everywhere you can ride you can drive him. Definitely get your saddle fit checked by a real professional too so you know 100% that it fits, don't just take someone's word. A horse in pain can't learn anything. Then you get back on him and introduce everything you've been working on under saddle again. If you've done the driving right, everything should still be there and you can just get on and go pretty much.
With ground driving you can get a horse pretty darn broke long before you ever swing a leg over, and then when you go to get on they already know their job, and they just have to adjust to a person on their back. Not a person on their back AND trying to balance AND steering AND new sights and sounds AND that spooky shadow over there. Etc etc etc. It can quickly get VERY overwhelming for a young horse. And that's another important thing, really reading the horse and paying attention so you don't put too much on them at once. It all should be very simple, easy, step by step, building onto the next thing.
Ground driving is that link between ground work and getting on, you couldn't pay me to skip that step!
Last edited by albertaeventer; 07-18-2013 at 02:21 PM.