Just casting about for ideas. I realized last night that one of my students has real issues with excessively stiff wrists. This kid (beginner at piano) has dyspraxia, along with some eyesight difficulties and hearing loss. The eyesight and hearing haven't proven to be issues so far.
His wrists are very stiff at the piano, so he is playing notes, and playing songs he knows, but without much control. I pointed out to him that he has wrists and that they can bend, I think this went right over his head! We tried knocking on a door (knock! knock!) and there was much pummelling going on, but absolutely locked and rigid wrists, all movement was from the elbow.
I realize now this had been an issue some weeks back when we tried chime bars. He gets as far as holding the stick, but then he can't do a bounce so the chime bar immediately mutes. I'm not a percussion teacher, I just use the chimes as an easy pre-piano stage, so at that point I just put them away and didn't worry about it.
Last night, with his permission, I actually took his hand and arm and manipulated his hand so he could see the wrist joint move. I was amazed at how much muscle effort was going into keeping is stiff and I had to ask him to relax several times so it could bend. I didn't actually fight his muscles, I just wanted to see how much tension was happening. Answer - lots!
I don't normally do hands-on teaching of the Irina Gorin sort, but I'm thinking it may be needed in this case.