The horse just had his wolf teeth pulled and his teeth floated. I will first off be checking for any body soreness, an ill fitting saddle, bit or bridle. So I will be ruling out any physical causes.
I personally believe that it's not going to be physical.
That this young horse has not learned yet to give to and accept the bit (snaffle and now french link snaffle that his owners' are using). And I also feel he has learned the bad habit of pulling the reins out of his young rider's hands and getting away with it (as he does chomp on the bit when the mother rides, but does not pull on the reins). So, I am going to work on softening his jaw and neck, teaching him to accept the bit and to work in a steady frame. I am also not going to allow him to pull the reins out of my hands, and I will give only when he softens and does not pull.... but I have two ways to go about that - I can ride him without any direct contact so he has nothing to lean and pull against or I can be unforgiving and release the tension when he stops pulling. (I don't really like the idea of riding with contact....)
But I am just looking for personal opinions as to what other's have done so I am well educated and prepared to find what works to help this horse.
Of course, I will be helping his young rider learn to apply these methods to her riding and to cope and positively and persistently to correct his behavior.
Open to personal experiences.