I work with my dd on a knuckleball as an alternative to her change up. She is 10. Up until today it has never been a true knuckleball - it has spin. However it has been a reliable off speed pitch whenever she struggles with her change up.
At any rate, I've been drilling her to try and make sure her thumb is the last thing to touch the ball on release and today she actually pitched three true knuckleballs that danced!
We came in afterward and she was so excited she told my wife "I threw knuckleballs that actually 'knucked'"! My wife cracked up - "is there such a verb as 'to knuck'?". I think there is now.