Advice on stamping out bad playing techniques in students that don't want to change
I have a 10y/o student that plays with a very bouncy arm. Like his elbows are flapping when he plays and his wrists are bounding up and down. I continue to remind him and try to show him the right technique, and he will do it for a note or two, but with a very bad attitude, while insisting his way is better and it's easier. When I get him to play with better technique, he plays comically badly on purpose to show me that his technique is better. I try to explain to him that with all the bouncing his hand will move around a lot and it will be very difficult to play the right notes without looking at your hands, but I'm having trouble making headway with him. He's only been playing for about 6 months, so I don't want to be too pushy and make the experience unenjoyable, but I think this way of playing will only cause him harm in the future and should be corrected as early as possible.
It's not that he can't understand what the right position is, it's that he thinks the right way to play is stupid and I'm getting pushback. Anyone dealt with something similar?