Building on the ideas of one of my previous articles: Why extrinsic rewards are so bad for motivation, you might have missed this great article from string teaching magazine, The Strad.
In it, a parent delves into some research about bribes, motivation and practice to come up with some really clear suggestions which you can use with your parents.
You can read the full article here:
Do you agree? Are extrinsic rewards OK in small doses?