One suggestion that Chemaine made was to counter flex him every single time his head snaps up. As soon as he softens to the new bend, I can allow him to slowly swing back to a correct bend. To show him that changing the bend doesn't have to be hard, she also suggested I throw in a counter bend every now and then even when he's being good.
One of the reasons Izzy resists the change of bend is because he is still trying to find his balance. Changing the bend too quickly throws him off balance which makes him feel less than confident, and if there is anything I've learned about this horse, he does not like to feel unsuccessful.
I put together a chain of 10-meter half circles that I am now doing at the walk every time I get on. Izzy is getting so good at the change of bend that he is now shifting his own weight as soon as I ask for the counter bend. After we do it at the walk, I do it at the trot, but the circles are usually more like 15-meters.
I did this exercise on Saturday. After a few rounds at both walk and trot, I did 20-meter circles at A, down to E, down to C, down to B, and then back to A. I followed those by doing 20-meter trot circles at A, cross the diagonal, 20-meter trot circle at C, and cross the diagonal. Then, we finished up by doing 10-meter half circles to centerline, trot down centerline to another 10-meter half circle to get back on the rail. I kept repeating the half circles at various places down the rail and the centerline.
By the time we were finished, Izzy was pretty supple from head to toe. Now, we need to get all of the transitions crisper and looking more "obedient." Once we get that, we might be ready for a schooling show.