My 12-year-old son's piano lesson is tomorrow morning and I am preparing for the battle. He has not practiced since his 30-minute lesson last week. If he has trouble with it I will not be much help. I'll try, but I only took piano lessons for a year and it was a long time ago. The song he is working on is at an intermediate level. He always tells me that if he practices it wrong then it will be a bigger problem for him than if he just waits until his next lesson.
I would suggest he raise this issue with his teacher and make a plan for how to deal with it if this situation arises. If he or she would prefer he doesn't play the newest piece he should certainly have a repertoire of earlier pieces or scales that he could practice to keep up his muscle memory.
My personal take is that part of the process of learning is that yes, sometimes you learn something wrong. Just like many of our early readers ended up mispronouncing all sorts of words over time that corrects itself.
