We recently purchased a 12 year old pony gelding for my 8 year old daughter. All he seems to want to do is follow someone leading him. When she tries to get him going on her own, he plants his feet and ignores her or tosses his head up and down. We have tried a snaffle bit as well as a curved bit with a spinner in the middle with no luck. I'm going to borrow a hackamore and try it this week. In every other way he is great. He loads, leads, and does not spook. My daughter has taken some lessons, but is still basically a beginner rider. I'm not sure if he is a good fit, because she struggles with him so much.
What was the history you were given on the pony when you purchased him? Did you do a test ride prior to the purchase - if so was it done on lead or with an independent rider? Was a PPE done? Is your daughter still taking lessons and, if so, have you had her instructor work with her on this pony or is she still only riding lesson horses during her sessions? Have you tried having a more advanced rider take a ride or two on him and, if so, does he behave the same or does he do what is asked?
This could be a pony issue, it could be a rider issue or it could be a combination of the two (quite likely - a rider that lacks confidence can very easily be read and taken full advantage of by a clever pony)
Teach him to long rein/ground drive, as this will teach him the cues to walk trot ect with out some one leading him, or when you take them out maybe start walking at the shoulder and then slowly move back until he is brave enough to not have to follow some one, I know you pony probably won't be a Shetland but I think it is a quite common problem in Shetlands.
We went to an auction with a friend. (I know not smart) My daughter has always wanted a white horse and when she saw him she went crazy. He was suppose to be kid gentle and I guess he is as long as the kid wants to be lead around. She was taking lessons, but her instructor moved away. I am trying to find her a new one.
I would definitely get another trainer before trying to do too much with this pony. At least where I am, auctions give you little to no real information about the horses you buy and often horses are at auction for a reason (granted where I am the horse industry is thriving more so than many areas of the states- I don't know where you are) and there are health / behavioural problems lurking. It doesn't sound as if you and your daughter have a lot of experience working with horses, and I would be worried that this pony might act out in a way that could hurt you or your daughter without experienced help.