If you don't mind me bragging a little.
Well I've had incredible difficulty with my mare, Paris, in getting her to go in a nice frame ( she is normally very hard to get into a frame and she is ALWAYS above the vertical line.). I've struggled with it for a few months and I pretty much tried EVERYTHING but then I figured out lunging her for 10 minutes before riding her works great! She is much more eager to learn, she has better gaits and she is an all around easier ride! It's amazing! We even have a better bond!
I highly recommend lunging difficult horses! :)