Thanks everyone:) This horse has a lot of energy so I think the plan will be too work with him on the ground after lunging awhile. Do a lot more desensitizing, and we'll be starting from the very beginning. I really wish the trainer hadn't abandoned us when we had such high hopes for this gelding. But I think he's still gotta chance at least with my sister because she's been riding since she was 9. Anymore suggestions are welcome:) I'll try and update on progress.
Hi, I too am with Kevin & others. We need much more info before we can offer you any specific advice, but it sounds like you're young & not very experienced(no offense meant if you're not, just going on what you've said), so finding a *GOOD* trainer would be the best move.
As for your sister, without knowing what her experience/age is, all I will say is there are riders & there are trainers... & there are good trainers. They don't all necessarily equate to the same thing at all. For eg. I've been riding since I was 5yo, but it wasn't until I was around 20yo that I *started* to learn how to train horses. I would ensure you get the horse well started with a good rider and trainer, especially if he's already gained some bad experiences & attitudes through that 'trainer'.
I don't reckon you're necessarily any worse off for the trainer 'abandoning' you like that, because it sounds like she probably wasn't much chop to be saying/doing that sort of thing. The horse may have become more 'crazy' the longer he was with her.
As for "work with him on the ground after lunging awhile" I don't agree with *what I perceive* this approach to be. Firstly, 'groundwork' should start at the very basics, of which 'lunging' is one of the higher 'levels'(perhaps think of starting at kindergarten & lunging is 'grade 3'). So I would definitely not try to start at lunging, unless he's already mastered the first few 'grades'. Also it sounds like(again, no offense if I got it wrong) you mean to lunge him to tire him out first, before doing other stuff. Number of reasons why I disagree with that approach(including 'lots of energy' may be nervous/frightened behaviour), but mainly, especially when considering an uneducated horse, you want to do everything in your power to create a great attitude towards you & your games & toys. So I don't reckon forcing the horse to run in endless circles is productive for this. He's more likely to learn to hate the 'work' you make him do that way.